A magnetic-thermal dual-responsive green nanoemulsifier and its preparation method

Abstract

The present invention provides a magnetothermal dual-responsive green nanoemulsifier and a preparation method thereof, belonging to the technical field of emulsifiers. The preparation method comprises the following steps: S1. preparing Fe3O4 nanoparticles; S2. preparing Fe3O4@SiO2 nanoparticles; S3. preparing Fe3O4@SiO2@NH2 nanoparticles; S4. preparing Fe3O4@SiO2@Br nanoparticles; and S5. preparing Fe3O4@SiO2@PNIPAM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier. The preparation method of the present invention is simple and controllable, with a short cycle time. The resulting nanoemulsifier has good emulsification effect, high stability, and is environmentally friendly. It has efficient magnetothermal responsiveness and can be recycled and reused.

Description

Technical Field

[0001] The present invention relates to the technical field of emulsifiers, and in particular to a magnetothermal dual-responsive green nanoemulsifier and a preparation method thereof. Background Art

[0002] In order to improve the recovery rate, most oil fields use chemical flooding methods, mainly including surfactant flooding, polymer flooding and emulsion flooding. However, due to the high cost and easy adsorption of surfactant flooding by rocks, and the poor shear resistance and temperature resistance of polymer flooding, attention has gradually shifted to emulsion flooding in recent years.

[0003] However, most of the current methods for preparing nanoemulsifiers are complicated, have long cycles, and are costly, and the emulsifiers produced are difficult to recycle. Therefore, there is still a need to find a simple, controllable, and short-cycle preparation method to obtain a nanoemulsifier with good emulsification effect and recyclable properties. Summary of the Invention

[0004] In response to one or more technical problems existing in the prior art, the present invention provides a magnetothermal dual-responsive green nanoemulsifier and a preparation method thereof. The preparation method of the present invention is simple and controllable, with a short cycle. The prepared nanoemulsifier has good emulsification effect, high stability, and is environmentally friendly. It has efficient magnetothermal responsiveness and can realize the recycling and reuse of the nanoemulsifier.

[0005] In a first aspect, the present invention provides a method for preparing a magnetothermal dual-responsive green nanoemulsifier, the preparation method comprising the following steps:

[0006] S1. A mixture of ferric salt and ferrous salt is dissolved in water, reacted in a N2 gas atmosphere under alkaline conditions to obtain Fe3O4 nanoparticles;

[0007] S2. The Fe3O4 nanoparticles are dispersed in a first solvent, a basic catalyst, an organosilicon compound is added, and the reaction is carried out at room temperature until the system changes from black to dark gray to obtain Fe3O4@SiO2 nanoparticles;

[0008] S3. After the Fe3O4@SiO2 nanoparticles are pretreated, dispersed in a second solvent, a first acid binding agent, an aminosilane solution is added, and after a first reaction, Fe3O4@SiO2@NH2 nanoparticles are obtained;

[0009] S4. The Fe3O4@SiO2@NH2 nanoparticles are dispersed in an organic solvent, a second acid binding agent and an initiator are added, and the second reaction is performed to obtain Fe3O4@SiO2@Br nanoparticles;

[0010] S5. Dispersing Fe3O4@SiO2@Br nanoparticles and polymerized monomers in water to obtain a first mixed solution; dissolving CuBr2 and L-ascorbic acid in water, and adding an organic ligand to obtain a second mixed solution; and mixing the first and second mixed solutions under nitrogen protection, and undergoing a third reaction to obtain Fe3O4@SiO2@PNIP AM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier.

[0011] Preferably, in step S1, a mixture of ferric salt and ferrous salt is dissolved in water, and an alkali solution is added to the mixture under a N2 atmosphere until the pH is 9.5 to 10, and the mixture is reacted at 65 to 70°C until black particles appear, thereby obtaining Fe3O4 nanoparticles;

[0012] Preferably, the molar ratio of the iron element in the ferric salt and the ferrous salt is 2:1.

[0013] Preferably, in step S2, the usage ratio of the Fe3O4 nanoparticles, the alkaline catalyst, and the organosilicon compound is (0.5-0.6) g: (2-3) mL: (1.5-2) mL;

[0014] Preferably, the first solvent is a mixture of anhydrous ethanol and water; preferably, the volume ratio of anhydrous ethanol to water in the first solvent is 3:1.

[0015] Preferably, the alkaline catalyst is aqueous ammonia with a mass fraction of 20 to 28%.

[0016] Preferably, the organosilicon compound is ethyl orthosilicate.

[0017] Preferably, in step S3, the Fe3O4@SiO2 nanoparticles are pretreated and then dispersed in a second solvent, a first acid binding agent and an aminosilane solution are added, the pH is adjusted to 8-10, and the mixture is reacted at 65-70°C for 4-12 hours to obtain Fe3O4@SiO2@NH2 nanoparticles.

[0018] Preferably, in step S4, the Fe3O4@SiO2@NH2 nanoparticles are dispersed in an organic solvent, a second acid binding agent is added, and the mixture is stirred in an ice-water bath at 4-6°C for 10-20 minutes. An initiator is added, and the mixture is reacted at 0-6°C for 1-2 hours and then at room temperature for 4-12 hours to obtain Fe3O4@SiO2@Br nanoparticles.

[0019] Preferably, in step S5, under N2 protection, the first mixed solution and the second mixed solution are mixed and reacted at room temperature for 3 to 7 hours to obtain Fe3O4@SiO2@PNIPAM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier.

[0020] Preferably, in step S3, the pretreatment is to soak the Fe3O4@SiO2 nanoparticles in piranha solution for 10 to 20 minutes;

[0021] The piranha solution is obtained by mixing hydrogen peroxide solution and concentrated sulfuric acid in a volume ratio of 1:3; the mass fraction of the hydrogen peroxide solution is 30%.

[0022] Preferably, in step S3, the usage ratio of the Fe3O4@SiO2 nanoparticles, the first acid binding agent, and the aminosilane is (0.5-0.6) g: (0.05-0.06) mL: (0.3-0.45) mL.

[0023] Preferably, in step S4, the usage ratio of the Fe3O4@SiO2@NH2 nanoparticles, the second acid binding agent, and the initiator is (0.5-0.6) g: (0.3-0.4) mL: (0.2-0.3) mL.

[0024] Preferably, in step S5, the mass ratio of the Fe3O4@SiO2@Br nanoparticles, polymerization monomer, CuBr2, L-ascorbic acid, and organic ligand is 0.2:(0.7-3):(0.05-0.07):(0.015-0.020):(0.13-0.15).

[0025] Preferably, in step S3, the aminosilane solution is obtained by mixing aminosilane and water in a volume ratio of 3:5.

[0026] Preferably, in step S3, the second solvent is anhydrous ethanol.

[0027] Preferably, in step S3, the first acid binding agent is triethanolamine or triethylamine.

[0028] Preferably, in step S3, the aminosilane is 3-aminopropyltriethoxysilane.

[0029] Preferably, in step S4, the organic solvent is toluene; and the second acid binding agent is pyridine.

[0030] Preferably, in step S4, the initiator is 2-bromoisobutyl bromide and / or 2-bromo-2-methylpropionyl bromide.

[0031] Preferably, in step S5, the polymerizable monomer is N-isopropylacrylamide.

[0032] Preferably, in step S5, the organic ligand is one or more of tris(2-dimethylaminoethyl)amine, tris(2-aminoethyl)amine, and pentamethyldiethylenetriamine.

[0033] In a second aspect, the present invention provides a magnetothermal dual-responsive green nanoemulsifier, which is prepared using the preparation method described in the first aspect.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] The green, magnetothermal-responsive nanoemulsifier (Fe3O4@SiO2@PNIPAM nanoparticles) produced by this invention exhibits excellent emulsification, high stability, and environmental friendliness. Its efficient magnetothermal response allows for the recycling of the nanoemulsifier. The polymer (PNIPAM) content in this emulsifier can reach up to 42.5% of the Fe3O4@SiO2 nanoparticle mass, and it exhibits an excellent LCST (critical solution temperature) of approximately 32°C. In this emulsifier, the polymer PNIPAM is grafted onto the outer layer of Fe3O4@SiO2. PNIPAM has good stretchability in water and strong hydrophilicity at room temperature. After emulsification, the outer layer adsorbs water molecules to easily form a relatively stable O / W emulsion. After adding a magnet to the outside of the emulsion, the Fe3O4@SiO2@PNIPAM nanoparticles are separated, causing the emulsion to break. When the temperature is above the LCST (critical solution temperature), the Pickering emulsion will break. When the temperature returns to below the LCST (critical solution temperature), it can be emulsified again and still form a stable emulsion. The Pickering emulsion can be arbitrarily switched between the emulsified and demulsified states by regulating temperature and magnetic field, and the Pickering emulsion can be separated and recovered through the magnetic field, providing a way to recycle and reuse the Pickering emulsion, in line with the concept of green environmental protection, and has good application prospects in the field of intelligent Pickering emulsion oil recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a schematic diagram of the preparation process of a magnetothermal dual-responsive green nanoemulsifier provided by the present invention;

[0038] Figure 2 IR spectra of Fe3O4 nanoparticles, Fe3O4@SiO2 nanoparticles, Fe3O4@SiO2@Br nanoparticles, and Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) according to Example 3 of the present invention;

[0039] Figure 3is a scanning electron microscope image of the Fe3O4@SiO2 nanoparticles of Example 3 of the present invention (magnification is 5000 times);

[0040] Figure 4 is a scanning electron microscope image of the Fe3O4@SiO2@PNIPAM nanoparticles of Example 3 of the present invention (magnification is 5000 times);

[0041] Figure 5 This is a transmission electron micrograph of the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention (magnification: 8000 times);

[0042] Figure 6 It is a part of the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention ( Figure 5 Enlarged transmission electron micrograph (circled part);

[0043] Figure 7 3 is the XRD pattern of Fe3O4 nanoparticles, Fe3O4@SiO2 nanoparticles, and Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention;

[0044] Figure 8 The differential thermal-thermogravimetric analysis graphs of the Fe3O4 nanoparticles, Fe3O4@SiO2 nanoparticles, Fe3O4@SiO2@Br nanoparticles of Example 3 of the present invention, the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-1) of Example 1, the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-2) of Example 2, and the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3;

[0045] Figure 9 3 is a room temperature hysteresis curve diagram of Fe3O4 nanoparticles, Fe3O4@SiO2 nanoparticles, and Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention;

[0046] Figure 10 This is a physical picture of the magnetic field control of the emulsion formed by Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) in Example 3 of the present invention;

[0047] Figure 114 is a graph showing the critical solution temperature of the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-1) of Example 1, the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-2) of Example 2, and the Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention;

[0048] Figure 12 This is a photo of the temperature control of the Fe3O4@SiO2@PNIPAM nanoparticle (emulsifier F-3) 0.1 wt% emulsion according to Example 3 of the present invention;

[0049] Figure 13 This is a photo of the magnetic separation of Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention at 25°C and 45°C;

[0050] Figure 14 This is a curve of the change in water separation rate within 24 hours of emulsions with different concentrations (0.01wt%, 0.1wt% and 0.5wt%) of Fe3O4@SiO2@PNIPAM nanoparticles (emulsifier F-3) of Example 3 of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0052] In a first aspect, the present invention provides a method for preparing a magnetothermal dual-responsive green nanoemulsifier, the preparation method comprising the following steps:

[0053] S1. A mixture of ferric salt and ferrous salt is dissolved in water, reacted in a N2 gas atmosphere under alkaline conditions to obtain Fe3O4 nanoparticles;

[0054] S2. The Fe3O4 nanoparticles are dispersed in a first solvent, a basic catalyst, an organosilicon compound is added, and the reaction is carried out at room temperature until the system changes from black to dark gray to obtain Fe3O4@SiO2 nanoparticles;

[0055] S3. After the Fe3O4@SiO2 nanoparticles are pretreated, dispersed in a second solvent, a first acid binding agent, an aminosilane solution is added, and after a first reaction, Fe3O4@SiO2@NH2 nanoparticles are obtained;

[0056] S4. The Fe3O4@SiO2@NH2 nanoparticles are dispersed in an organic solvent, a second acid binding agent and an initiator are added, and the second reaction is performed to obtain Fe3O4@SiO2@Br nanoparticles;

[0057] S5. Dispersing Fe3O4@SiO2@Br nanoparticles and polymerized monomers in water to obtain a first mixed solution; dissolving CuBr2 and L-ascorbic acid in water, and adding an organic ligand to obtain a second mixed solution; and mixing the first and second mixed solutions under nitrogen protection, and undergoing a third reaction to obtain Fe3O4@SiO2@PNIP AM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier.

[0058] It should be noted that Fe3O4@SiO2 nanoparticles are Fe3O4 nanoparticles with SiO2 coated on the surface, Fe3O4@SiO2@NH2 nanoparticles are Fe3O4@SiO2 nanoparticles with multi-molecular layer amino modification on the surface, Fe3O4@SiO2@Br nanoparticles are Fe3O4@SiO2 nanoparticles with bromine modification on the surface, and Fe3O4@SiO2@PNIPAM are Fe3O4@SiO2 nanoparticles with polymer (PNIPAM) grafted on the surface.

[0059] It should be noted that the first solvent in the present invention mainly plays a dispersing role, and there is no particular limitation on its usage, as long as it can disperse the Fe3O4 nanoparticles evenly.

[0060] The present invention first prepares Fe3O4 nanoparticles by a chemical precipitation method, then uses the Fe3O4 nanoparticles and an organosilicon compound as raw materials to prepare Fe3O4@SiO2 nanoparticles with silicon dioxide coated on the surface under the condition of an alkaline catalyst; then uses the pretreated Fe3O4@SiO2 nanoparticles and an aminosilane solution as raw materials to prepare Fe3O4@SiO2@NH2 nanoparticles with multi-molecular-layer amino-modified surfaces under the action of a first acid-binding agent; then uses the Fe3O4@SiO2@NH2 nanoparticles and an initiator as raw materials to prepare Fe3O4@SiO2@Br nanoparticles under the action of a second acid-binding agent; finally, uses the Fe3O4@SiO2@Br nanoparticles, a polymerization monomer, CuBr2, L-ascorbic acid, and an organic ligand as raw materials to prepare Fe3O4@SiO2@PNIPAM nanoparticles with a polymer grafted on the surface, i.e., the magnetothermal dual-responsive green nanoemulsifier of the present invention; the preparation method of the present invention is simple, controllable, and has a short cycle.

[0061] According to some preferred embodiments, in step S1, a mixture of ferric salt and ferrous salt is dissolved in water, and an alkali solution is added to the mixture under a N2 atmosphere until the pH is 9.5 to 10, and the mixture is reacted at 65 to 70°C until black particles appear, thereby obtaining Fe3O4 nanoparticles;

[0062] The present invention does not limit the types of ferric salts and ferrous salts, as long as they are soluble ferric salts and soluble ferrous salts; for example, the ferric salt can be ferric chloride hexahydrate, ferric sulfate, or ferric nitrate, and the ferrous salt can be ferrous chloride tetrahydrate or ferrous sulfate.

[0063] It should be noted that the present invention does not specifically limit the type and concentration of the alkali solution. The alkali solution can be ammonia water, sodium hydroxide solution, potassium hydroxide solution, but is not limited thereto; as long as the pH of the reaction system can be adjusted to the target range;

[0064] In a specific embodiment of the present invention, 2.7 g of FeCl3·6H2O and 1.075 g of FeCl2·4H2O are weighed, added to 50 mL of deionized water, and then transferred to a three-necked flask and stirred with a magnet. The air in the flask is evacuated and N2 is introduced to ensure that the entire reaction is carried out in an N2 environment. 25% NH3·H2O is added dropwise to the mixed solution until the solution pH = 10. The system temperature is raised to 70°C and the reaction is carried out for half an hour under vigorous stirring. As the reaction proceeds, the system gradually turns black and black Fe3O4 particles appear at the bottom. Finally, the system is centrifuged, washed with deionized water multiple times, dried, and separated with a magnet to obtain pure Fe3O4 nanoparticles.

[0065] According to some more preferred embodiments, the molar ratio of the iron element in the ferric salt and the ferrous salt is 2:1.

[0066] According to some preferred embodiments, in step S2, the usage ratio of the Fe3O4 nanoparticles, the alkaline catalyst, and the organosilicon compound is (0.5-0.6) g: (2-3) mL: (1.5-2) mL.

[0067] The purpose of step S2 of the present invention is to coat a layer of SiO2 on the surface of the Fe3O4 nanoparticles to obtain Fe3O4@SiO2 nanoparticles, so that the surface of the Fe3O4@SiO2 nanoparticles can be subsequently amino-modified; without this step, the amino modification on the surface of the Fe3O4 nanoparticles cannot be achieved.

[0068] In some specific embodiments of the present invention, 0.6 g of Fe3O4, 60 mL of H2O, 180 mL of anhydrous ethanol, and 2 to 3 mL of ammonia water (the mass fraction of the solute is 20 to 28%) are weighed and added to a three-necked flask and ultrasonically dispersed for 30 minutes. Then, 1.8 mL of tetraethyl orthosilicate (TEOS) is added. The mixture is magnetically stirred at room temperature until the color of the reaction system gradually changes from black to dark gray, indicating that SiO2 particles have been successfully coated on the surface of the Fe3O4 particles. After the reaction, the solid particles are washed multiple times with ethanol and deionized water to remove unreacted NH3·H2O and tetraethyl orthosilicate (TEOS), and then dried in a 60°C oven overnight to obtain Fe3O4@SiO2 nanoparticles.

[0069] According to some preferred embodiments, the first solvent is a mixture of anhydrous ethanol and water.

[0070] According to some more preferred embodiments, the product ratio of anhydrous ethanol to water in the first solvent is 3:1.

[0071] According to some preferred embodiments, the alkaline catalyst is aqueous ammonia with a mass fraction of 20 to 28%.

[0072] The present invention uses ammonia water to provide an alkaline environment for the reaction and also acts as a catalyst in the reaction process. Without the addition of ammonia water, Fe3O4@SiO2 nanoparticles cannot be obtained.

[0073] According to some preferred embodiments, the organosilicon compound is tetraethyl orthosilicate (TEOS).

[0074] According to some preferred embodiments, in step S3, the Fe3O4@SiO2 nanoparticles are pretreated and then dispersed in a second solvent, a first acid binding agent and an aminosilane solution are added, the pH is adjusted to 8-10, and the mixture is reacted at 65-70°C for 4-12 hours to obtain Fe3O4@SiO2@NH2 nanoparticles.

[0075] It should be noted that the second solvent in the present invention mainly plays a dispersing role, and there is no particular limitation on its amount, as long as it can evenly disperse the Fe3O4@SiO2 nanoparticles.

[0076] The purpose of the pretreatment of the present invention is to produce a large number of hydroxyl groups on the surface of the Fe3O4@SiO2 nanoparticles; if no pretreatment is performed, the number of hydroxyl groups on the surface of the Fe3O4@SiO2 nanoparticles is small, the aminosilane cannot fully react with the Fe3O4@SiO2, and the yield of the Fe3O4@SiO2@NH2 nanoparticles is low, and the subsequent initiator grafting amount is small, resulting in a low polymer content in the final product.

[0077] The aminosilane solution of the present invention is a mixture of aminosilane and water, wherein the water provides a hydrolysis condition for the aminosilane, converting the ethoxy groups in the aminosilane into hydroxyl groups, which then undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the treated Fe3O4@SiO2 nanoparticles to form Si-O-Si bonds. The products of the APTES hydrolysis also condense with each other to form polysiloxanes, ensuring multi-layer amino modification of the Fe3O4@SiO2 nanoparticle surface. Without the addition of water, the siloxane bonds would directly react with the hydroxyl groups on the Fe3O4@SiO2 surface, achieving amino modification. However, in anhydrous conditions, the siloxane bonds do not react with each other, and condensation between 3-aminopropyltriethoxysilane (APTES) molecules does not occur, resulting in only a single-layer amino modification. Compared to single-layer amino modification, multi-layer amino modification has a higher amino density and better controllability; however, the controllability and reproducibility of single-layer amino modification experiments are poor.

[0078] The first acid-binding agent in the present invention is mainly used to absorb the acidic substances generated during the reaction and provide a weakly alkaline environment to ensure that the multi-layer amino modification reaction can proceed smoothly. If the first acid-binding agent is not added, the amino modification reaction will be incomplete, the modification effect will be poor, and the obtained product will be impure.

[0079] In some specific embodiments of the present invention, 0.5g of Fe3O4@SiO2 nanoparticles are soaked in a piranha solution (30% hydrogen peroxide solution: concentrated sulfuric acid = 1:3) for 10 minutes. Then, 25mL of anhydrous ethanol and 0.05mL of a first acid-binding agent are added and ultrasonically dispersed. A mixed solution of 0.3mL of aminosilane and 0.5mL of H2O is then added. The pH is adjusted to 8-10 with aqueous ammonia, and the mixture is reacted at 65°C for 4-12 hours. After the reaction, the mixture is centrifuged, washed with ethanol, and dried in an oven at 70°C to obtain Fe3O4@SiO2@NH2 nanoparticles.

[0080] According to some preferred embodiments, in step S4, the Fe3O4@SiO2@NH2 nanoparticles are dispersed in an organic solvent, a second acid binding agent is added, and the mixture is stirred in an ice-water bath at 4-6°C for 10-20 minutes. An initiator is added, and the mixture is reacted at 0-6°C for 1-2 hours and then at room temperature for 4-12 hours to obtain Fe3O4@SiO2@Br nanoparticles.

[0081] It should be noted that the organic solvent in the present invention mainly plays a dispersing role, and there is no particular limitation on its usage, as long as it can evenly disperse the Fe3O4@SiO2@NH2 nanoparticles.

[0082] The second acid-binding agent in the present invention is mainly used to absorb the acidic substances generated during the reaction and provide a weakly alkaline environment to ensure that the initiator can react with the amino groups on the surface of the Fe3O4@SiO2@NH2 nanoparticles. If the second acid-binding agent is not added, the reaction rate will be slow, the reaction will not be complete, and the product obtained will be impure.

[0083] In some specific embodiments of the present invention, 0.5 g of Fe3O4@SiO2@NH2 nanoparticles are weighed and dispersed in 25 mL of toluene, and then 0.05 mL of a second acid binding agent is added. The mixture is stirred in an ice-water bath at 4 to 6°C for 10 to 20 minutes, and then 0.2 mL of an initiator is added. The mixture is reacted at 0 to 6°C for 1 hour, then transferred to room temperature and continued to react for 4 to 12 hours. The mixture is centrifuged, washed with toluene, and dried in an oven at 70°C to obtain Fe3O4@SiO2@Br nanoparticles.

[0084] According to some preferred embodiments, in step S5, under N2 protection, the first mixed solution and the second mixed solution are mixed and reacted at room temperature for 3 to 7 hours to obtain Fe3O4@SiO2@PNIPAM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier.

[0085] According to some preferred embodiments, in step S3, the pretreatment is to soak the Fe3O4@SiO2 nanoparticles in piranha solution for 10 to 20 minutes;

[0086] The piranha solution is obtained by mixing hydrogen peroxide solution and concentrated sulfuric acid in a volume ratio of 1:3; the mass fraction of the hydrogen peroxide solution is 30%.

[0087] Before performing multi-molecular-layer amino modification on the surface of Fe3O4@SiO2 nanoparticles, the present invention soaks the Fe3O4@SiO2 nanoparticles in a piranha solution to generate more hydroxyl groups on the surface of the Fe3O4@SiO2 nanoparticles, thereby ensuring that aminosilane can combine with sufficient hydroxyl groups during the multi-molecular-layer amino modification process, thereby achieving sufficient modification of all parts of the surface of the Fe3O4@SiO2 nanoparticles. If the piranha solution soaking treatment is not performed, the multi-molecular-layer amino modification effect on the surface of the Fe3O4@SiO2 nanoparticles is poor, the amount of amino grafting is small, and the grafting effect of the subsequent polymer is affected.

[0088] In some specific embodiments of the present invention, 0.0592 g CuBr2 and 0.0184 g L-ascorbic acid are added to a Schlenk I bottle and dissolved in 6 mL of water, and then 0.1424 mL of a first mixed solution of an organic ligand is added under magnetic stirring at 400 r / min; 0.2 g of Fe3O4@SiO2@Br nanoparticles are weighed and added to a Schlenk II bottle, and 0.7 to 3 g of a polymerized monomer is added and ultrasonically dissolved in 12 mL of water to obtain a second mixed solution; the Schlenk I bottle and the Schlenk II bottle are degassed by three pump aeration cycles, and then under the protection of N2 gas, the second mixed solution in the Schlenk II bottle is added to the Schlenk I bottle, the Schlenk I bottle is sealed, stirred at room temperature for 3 to 7 hours, centrifuged, washed three times with deionized water to remove unreacted substances, and vacuum dried at 50°C overnight to obtain Fe3O4@SiO2@PNIPAM nanoparticles, i.e., a magnetothermal dual-responsive green nanoemulsifier.

[0089] According to some preferred embodiments, in step S3, the usage ratio of the Fe3O4@SiO2 nanoparticles, the first acid binding agent, and the aminosilane is (0.5-0.6) g: (0.05-0.06) mL: (0.3-0.45) mL.

[0090] According to some preferred embodiments, in step S4, the usage ratio of the Fe3O4@SiO2@NH2 nanoparticles, the second acid binding agent, and the initiator is (0.5-0.6) g: (0.3-0.4) mL: (0.2-0.3) mL.

[0091] According to some preferred embodiments, in step S5, the mass ratio of the Fe3O4@SiO2@Br nanoparticles, polymerization monomer, CuBr2, L-ascorbic acid, and organic ligand is 0.2:(0.7~3):(0.05~0.07):(0.015~0.020):(0.13~0.15).

[0092] According to some preferred embodiments, in step S3, the aminosilane solution is obtained by mixing aminosilane and water in a volume ratio of 3:5.

[0093] According to some preferred embodiments, in step S3, the second solvent is anhydrous ethanol.

[0094] According to some preferred embodiments, in step S3, the first acid binding agent is triethanolamine (TEOA) or triethylamine (TEA).

[0095] According to some preferred embodiments, in step S3, the aminosilane is 3-aminopropyltriethoxysilane (APTES).

[0096] According to some preferred embodiments, in step S4, the organic solvent is toluene; and the second acid binding agent is pyridine.

[0097] According to some preferred embodiments, in step S4, the initiator is 2-bromoisobutyl bromide (BIBB) or 2-bromo-2-methylpropionyl bromide.

[0098] According to some preferred embodiments, in step S5, the polymerization monomer is N-isopropylacrylamide (NIPAM).

[0099] According to some preferred embodiments, in step S5, the organic ligand is tris(2-dimethylaminoethyl)amine (Me6TREN), tris(2-aminoethyl)amine (TREN), or pentamethyldiethylenetriamine (PMDETA).

[0100] In a second aspect, the present invention provides a magnetothermal dual-responsive green nanoemulsifier, which is prepared using the preparation method described in the first aspect.

[0101] The magnetothermal dual-responsive green nanoemulsifier (Fe3O4@SiO2@PNIPAM nanoparticles) prepared by the present invention has good emulsification effect, high stability, and is environmentally friendly. It has efficient magnetothermal responsiveness and can realize the recycling and reuse of the nanoemulsifier. The content of the polymer (PNIPAM) in the emulsifier can reach 42.5% of the mass of the Fe3O4 nanoparticles, and the LCST (critical solution temperature) is about 32°C. In this emulsifier, the polymer PNIPAM is grafted onto the outer layer of Fe3O4@SiO2. PNIPAM has good stretchability in water and strong hydrophilicity at room temperature. After emulsification, the outer layer adsorbs water molecules to easily form a relatively stable O / W emulsion. After adding a magnet to the outside of the emulsion, the Fe3O4@SiO2@PNIPAM nanoparticles are separated, causing the emulsion to demulsify. When the temperature is above the LCST (critical solution temperature) (32°C), the Pickering emulsion will demulsify. When the temperature returns to below the LCST (critical solution temperature), it can be emulsified again to still form a stable emulsion. The Pickering emulsion can be arbitrarily switched between the emulsified and demulsified states by regulating temperature and magnetic field, realizing the separation, recycling and reuse of the Pickering emulsion.

[0102] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention is further described below with reference to embodiments.

[0103] It should be noted that the materials and reagents in the present invention can be directly purchased on the market or synthesized by themselves, and there is no limitation on the specific models.

[0104] The performance of the embodiments and comparative examples of the present invention were tested according to the following methods:

[0105] 1) Fourier transform infrared spectroscopy (FT-IR) analysis: The determination was performed using an infrared spectrometer (Bruker-Tonsor 27); KBr pellets were used and the spectral measurement range was 400–4000 cm -1 ;

[0106] 2) Thermogravimetric analysis (TGA) was performed using a Discovery DSC25 differential scanning calorimeter in the temperature range of 25°C to 900°C at a heating rate of 10°C / min.

[0107] 3) X-ray diffraction (XRD): The crystal powder structure of the particles was measured using an X-ray diffractometer (D / MAX-2200, Rigaku Corporation, Japan) in the angle range of 10 to 80°;

[0108] 4) Scanning Electron Microscope (SEM) Analysis: The particle morphology was observed using a thermal field scanning electron microscope (Zeiss German SIGMA). Fe3O4@SiO2 nanoparticles and Fe3O4@SiO2@PNIPAM nanoparticles were first ultrasonically dispersed in anhydrous ethanol for 30 minutes. A drop of liquid was then dripped onto a silicon wafer. After the ethanol had completely evaporated, SEM analysis was performed.

[0109] 5) Transmission Electron Microscopy (TEM) Analysis: Analyzed using a JEM2100PLUS transmission electron microscope. Fe3O4@SiO2@PNIPAM nanoparticles were dispersed in ethanol. A carbon-coated copper mesh was placed in the dispersion and then removed and tested by evaporating the ethanol.

[0110] 6) Room temperature magnetic hysteresis curve (VSM): measured at room temperature by MPSS Squid VSM model vibrating sample magnetometer in the magnetic field range of -20000Oe to +20000Oe;

[0111] 7) Characterization of Pickering Emulsions: F-1, F-2, and F-3 were prepared into aqueous solutions of equal concentrations. Each solution was then emulsified with an equal volume of toluene dyed with Sudan III using an emulsifier (10,000 rpm, 2 min, 25°C) to produce a Pickering emulsion. The Pickering emulsions were allowed to stand for 24 h, and the phenomenon was observed and the water extraction rate was calculated. The water extraction rate calculation formula is:

[0112] X w =V1 / V0×100%

[0113] Where: X wis the desorption rate, %; V0 is the amount of nanoparticle solution added, mL; V1 is the amount of water precipitated from the lower layer of the emulsion after a period of time, mL; the smaller the desorption rate in the same time, the more stable the emulsion.

[0114] Example 1

[0115] Preparation of magnetic-thermal dual-responsive green nanoemulsifier F-1:

[0116] S1. Weigh 2.7 g of FeCl3·6H2O and 1.075 g of FeCl2·4H2O, add 50 mL of deionized water, and transfer to a three-necked flask. Stir with a magnet. Evacuate the air from the flask and introduce nitrogen to ensure that the entire reaction is carried out in an nitrogen environment. Add 25% NH3·H2O dropwise to the mixed solution until the pH of the solution reaches 10. Raise the system temperature to 70°C and react for 30 min with vigorous stirring. As the reaction proceeds, the system gradually turns black, and black Fe3O4 particles appear at the bottom. Finally, the mixture is centrifuged, washed with deionized water, dried, and separated with a magnet to obtain pure Fe3O4 nanoparticles.

[0117] S2. 0.6 g of Fe₃O₄, 60 mL of H₂O, 180 mL of anhydrous ethanol, and 2.4 mL of aqueous ammonia (25% by mass of the solute) were weighed and added to a three-necked flask and ultrasonically dispersed for 30 min. Then, 1.8 mL of tetraethyl orthosilicate (TEOS) was added and magnetically stirred at room temperature until the color of the reaction system gradually changed from black to dark gray, indicating that SiO₂ particles had successfully coated the surface of the Fe₃O₄ particles. After the reaction, the solid particles were washed with ethanol and deionized water to remove unreacted NH₃·H₂O and tetraethyl orthosilicate (TEOS) and dried in an oven at 60°C overnight to obtain Fe₃O₄@SiO₂ nanoparticles.

[0118] S3. Weigh 0.5g of Fe3O4@SiO2 nanoparticles and slurry in piranha solution (V 质量分数为30％的过氧化氢溶液 :V 浓硫酸 =1:3) for 10 min, then add 25 mL of anhydrous ethanol and 0.05 mL of triethanolamine (TEOA) and ultrasonically disperse, then add a mixed solution of 0.3 mL of 3-aminopropyltriethoxysilane (APTES) and 0.5 mL of H2O, adjust the pH to 9 with ammonia water, react at 65°C for 12 h, centrifuge after the reaction, wash with ethanol, and dry in an oven at 70°C to obtain Fe3O4@SiO2@NH2 nanoparticles;

[0119] S4. Weigh 0.5 g of Fe3O4@SiO2@NH2 nanoparticles and disperse them in 25 mL of toluene. Add 0.05 mL of pyridine and stir in a 5°C ice-water bath for 10 minutes. Then add 0.2 mL of 2-bromoisobutyl bromide and react at 6°C for 1 hour. Then, transfer the mixture to room temperature and continue the reaction for 12 hours. Centrifuge, wash with toluene, and dry in an oven at 70°C to obtain Fe3O4@SiO2@Br nanoparticles.

[0120] S5. Add 0.0592g CuBr2 and 0.0184g L-ascorbic acid to a Schlenk I flask and dissolve in 6mL of water. Then, add 0.1424mL of tris(2-dimethylaminoethyl)amine (Me6TREN) under magnetic stirring at 400r / min to obtain the first mixed solution. Weigh 0.2g of Fe3O4@SiO2@Br nanoparticles and add them to a Schlenk II flask. Add 0.75g of N-isopropylacrylamide (NIPAM) and dissolve them in 12mL of water under ultrasonication. , obtaining a second mixed liquid; the Schlenk I flask and the Schlenk II flask were degassed by three pump inflation cycles, and then under the protection of N2 gas, the second mixed liquid in the Schlenk II flask was added to the Schlenk I flask, the Schlenk I flask was sealed, stirred at room temperature for 7 hours, and after centrifugation, washed with deionized water three times to remove unreacted substances, and dried in vacuum at 50°C overnight to obtain Fe3O4@SiO2@PNIPAM nanoparticles, namely, magnetothermal dual-responsive green nanoemulsifier F-1.

[0121] Example 2

[0122] Preparation of magnetic-thermal dual-responsive green nanoemulsifier F-2:

[0123] The only difference from Example 1 is that in step S5 , the mass of N-isopropylacrylamide (NIPAM) is 1.5 g.

[0124] Example 3

[0125] Preparation of magnetic-thermal dual-responsive green nanoemulsifier F-3:

[0126] The only difference from Example 1 is that in step S5 , the mass of N-isopropylacrylamide (NIPAM) is 3 g.

[0127] Comparative Example 1

[0128] Comparative Example 1 is substantially the same as Example 3, except that: in step S2, no ammonia water is added;

[0129] In Comparative Example 1, Fe3O4@SiO2 nanoparticles could not be obtained because no ammonia water was added.

[0130] Comparative Example 2

[0131] Comparative Example 2 is substantially the same as Example 3, except that in step S3, the Fe3O4@SiO2 nanoparticles are not pre-treated by immersion in the piranha solution. The rest is the same as Example 1.

[0132] In Comparative Example 2, no pretreatment was performed before the surface multi-molecular layer amino modification, and the Fe3O4@SiO2 nanoparticles had few surface hydroxyl groups. The aminosilane could not fully react with Fe3O4@SiO2, resulting in a low yield of Fe3O4@SiO2@NH2 nanoparticles and a small amount of subsequent initiator grafting, resulting in a low polymer content in the final product.

[0133] Comparative Example 3

[0134] Comparative Example 3 is substantially the same as Example 3, except that triethanolamine is not added in step S3. The rest is the same as Example 1.

[0135] In Comparative Example 3, triethanolamine (the first acid-binding agent) was not added, which failed to provide a weakly alkaline environment for amination modification, resulting in a slow reaction rate and impure product.

[0136] Comparative Example 4

[0137] Comparative Example 4 is substantially the same as Example 3, except that water is not added in step S3. The rest is the same as Example 1.

[0138] In Comparative Example 4, since no water was added, the siloxane bonds would directly react with the hydroxyl groups on the Fe3O4@SiO2 surface to achieve amino modification. Under anhydrous conditions, the siloxane bonds would not react with each other, and condensation would not occur between the 3-aminopropyltriethoxysilane (APTES) molecules, so only a single-layer amino modification could be achieved.

[0139] Comparative Example 5

[0140] Comparative Example 5 is substantially the same as Example 3, except that pyridine is not added in step S4. The rest is the same as Example 1.

[0141] In Comparative Example 5, since pyridine (the second acid binding agent) was not added, the reaction rate was slow and the obtained product was impure.

[0142] Comparative Example 6

[0143] Comparative Example 6 is basically the same as Example 3, except that: in step S4, after adding 2-bromoisobutyl bromide (initiator), the reaction is directly carried out at room temperature for 12 hours. The rest is the same as Example 1.

[0144] In Comparative Example 6, the reaction was directly carried out at room temperature after the initiator was added. However, due to the high reactivity of 2-bromoisobutyl bromide, the reaction was easily denatured and inactivated at room temperature, which affected the reaction results, resulting in unsuccessful initiation and failure to synthesize Fe3O4@SiO2@Br.

[0145] Comparative Example 7

[0146] Comparative Example 7 is basically the same as Example 3, except that there is no step S2, and the rest is the same as Example 1.

[0147] In Comparative Example 7, there is no step of coating SiO2 on the surface of Fe3O4, so amino modification cannot be performed.

[0148] Comparative Example 8

[0149] Comparative Example 8 is basically the same as Example 3, except that there is no step S3, and the rest is the same as Example 1.

[0150] In Comparative Example 8, there is no process of amino modification on the surface of the Fe3O4@SiO2 nanoparticles, so that the initiator cannot be introduced into the surface of the Fe3O4@SiO2 nanoparticles subsequently, and the polymer grafting on the surface of the Fe3O4@SiO2 nanoparticles cannot be performed.

[0151] Comparative Example 9

[0152] Comparative Example 9 is substantially the same as Example 3, except that step S5 is omitted, and the rest is the same as Example 1;

[0153] In Comparative Example 9, no polymer grafting was performed on the surface of the Fe3O4@SiO2 nanoparticles, and a stable emulsion could hardly be formed.

[0154] Depend on Figure 2 It can be seen that the infrared curve of Fe3O4 nanoparticles is 575cm -1 The characteristic peak is the characteristic absorption peak of Fe-O bond. The infrared spectrum of Fe3O4@SiO2 nanoparticles is compared with the spectrum of Fe3O4. -1 There is a broad and strong peak at 880cm, which is the characteristic absorption peak of Si-O bond. -1 The asymmetric stretching vibration of Si-O-Si bond indicates that Fe3O4@SiO2 nanoparticles were successfully prepared. The Fe3O4@SiO2@Br nanoparticles have a -1 There is an additional absorption peak at 1686 cm, which is the stretching vibration peak of the amide bond NH. -1 and 1528cm -1The absorption peak at 2919 cm is the stretching vibration peak of NC=O, indicating that Fe3O4@SiO2@Br with acyl bromide groups grafted on the surface of Fe3O4@SiO2 was successfully prepared. After polymerization, Fe3O4@SiO2@PNIPAM nanoparticles -1 and 2850cm -1 New peaks appeared at , which are the asymmetric stretching vibrations of CH3 and CH2 in PNIPAM, indicating that PNIPAM was successfully grafted onto the surface of Fe3O4@SiO2.

[0155] Depend on Figure 3-4 It can be seen that the outer layer of Fe3O4@SiO2@PNIPAM particles is wrapped with a layer of polymer, resulting in a connection between the particles; compared with the unmodified Fe3O4@SiO2, the Fe3O4@SiO2@PNIPAM particles grafted with PNI PAM have become larger in outline, and the particle morphology has changed, showing morphological features similar to those of polymers, forming a core-shell structure of Fe3O4@SiO2 wrapped with polymers. Figure 5-6 It can be seen that the grafted product has a relatively obvious core-shell capsule structure. The particle size of the innermost layer of Fe3O4 is about 6 to 10 nm, the wall thickness of SiO2 is about 3 to 5 nm, and the thickness of the outermost layer of polymer PNIPAM is about 3 to 4 nm.

[0156] Depend on Figure 7 It can be seen that the XRD pattern of Fe3O4 shows obvious diffraction peaks at 30.2°, 35.6°, 43.2°, 53.5°, 57.3° and 62.7°, which is consistent with the standard card JCPDS 72-2303, proving that Fe3O4 with a cubic inverse spinel structure lattice has been effectively prepared. The characteristic diffraction peaks of Fe3O4@SiO2 are basically consistent with those of Fe3O4, because the amorphous structure of SiO2 does not affect the structure of Fe3O4, but due to the wrapping of SiO2 on the outside, the peak intensity is obviously not as good as that of Fe3O4; the characteristic peak position of Fe3O4@SiO2@PNIPAM has not changed, and the peak intensity is greatly weakened due to the grafting of polymers on the surface of Fe3O4@SiO2, which shows that the process of surface wrapping, modification and polymerization grafting of Fe3O4 does not affect the crystal structure of Fe3O4.

[0157] Depend on Figure 8It can be seen that the mass fractions of the residual solids of Fe3O4@SiO2 nanoparticles and Fe3O4@SiO2@Br nanoparticles at 900℃ are 75.6% and 59.8%, respectively, indicating that the amount of initiator grafted on the surface of Fe3O4@SiO2 is 15.8% of the mass of Fe3O4@SiO2 nanoparticles; emulsifiers F-1, F-2 and F-3 have obvious mass losses; and the mass losses of F-2 and F-3 are much greater than that of Fe3O4@SiO2@Br; the mass fractions of the residual solids of F-1, F-2 and F-3 at 900℃ are 57.8%, 33.6% and 17.3%, respectively. It can be calculated that the content of PNIPAM in F-1, F-2 and F-3 accounts for 2%, 26.2% and 42.5% of the mass of Fe3O4@SiO2 nanoparticles, respectively; further proving that Fe3O4@SiO2@PNIPAM was successfully prepared.

[0158] Depend on Figure 9 The saturation magnetizations of Fe₃O₄, Fe₃O₄@SiO₂, and emulsifier F-3 are 33.48 emu / g, 48.69 emu / g, and 63.45 emu / g, respectively. All three nanoparticles exhibit no hysteresis and possess superparamagnetic properties. While the magnetization of emulsifier F-3 is significantly weakened due to the SiO₂ coating and the grafting of the outermost PNIPAM layer, it still exhibits superparamagnetism, making it suitable for magnetic separation and recovery.

[0159] Depend on Figure 10 It can be seen that when the magnetic field is applied, the Pickering emulsion formed by emulsifier F-3 shows oil-water stratification. The oil-water interface is free of emulsion droplets, resulting in demulsification. The small amount of emulsifier F-3 particles originally in the emulsion are separated to the bottom by the magnetic field. When the magnetic field is removed and the emulsion is left to stand for 12 hours, it automatically floats back to its original position and re-emulsifies into a Pickering emulsion.

[0160] Depend on Figure 11 Emulsifiers F-1, F-2, and F-3 all exhibited temperature responsiveness, with phase transition temperatures of approximately 32°C, 33°C, and 34°C, respectively. When the ambient temperature is below the LCST (critical solution temperature), the thermosensitive amide bonds in PNIPAM can form hydrogen bonds with water, exhibiting hydrophilicity and allowing the PNIPAM chains to extend well in water. When the ambient temperature is above the LCST (critical solution temperature), the hydrogen bonds between the thermosensitive groups and water are broken, and the PNIPAM chains begin to shrink and squeeze out water molecules, transforming from a disk-like shape to a spherical shape, exhibiting a clumping phenomenon, and the solution becomes clear.

[0161] Depend on Figure 12It can be seen that emulsifier F-3 forms a uniform emulsion at 25°C, which is determined to be an O / W emulsion with good emulsification effect. After 24 hours of storage, a small amount of water precipitates from the lower layer, and the upper layer is still a stable O / W emulsion. It can be successfully placed for 1 month without demulsification. This is because the PNIPAM chains in emulsifier F-3 are in an extended state below the LCST (critical solution temperature). At this time, emulsifier F-3 is hydrophilic. The mass fraction of PNIPAM chains in Fe3O4 in emulsifier F-3 is the highest, so emulsifier F-3 is also the most hydrophilic. Emulsifier F-3 particles are more likely to adsorb a large number of water molecules, and the water molecules are firmly wrapped in the outer layer of emulsifier F-3, so the O / W emulsion formed is more stable. When an emulsion of emulsifier F-3 was placed at 50°C, it was found that the emulsion quickly demulsified, and the emulsifier F-3 particles aggregated in the upper oil phase. When re-emulsified at 25°C, a uniform emulsion was formed again. The reason for this phenomenon is that the PNIPAM chains in emulsifier F-3 expel water molecules above the LCST (critical solution temperature), resulting in agglomeration. It was also found that the PNIPAM chains at this time become more lipophilic, so almost all of the emulsifier F-3 precipitated in the oil phase. After the particles aggregated in the oil phase, the emulsion became unstable and demulsified. The emulsifier prepared by the present invention has excellent thermal response performance.

[0162] The experiment showed that at room temperature, the separation speed of emulsifier F-1, emulsifier F-2 and emulsifier F-3 particles in their aqueous solutions was similar when an external magnetic field was applied. However, at 45°C, the separation speed of emulsifier F-3 was the fastest. Figure 13 As can be seen, at 25°C, emulsifier F-3 disperses evenly in water. The applied magnetic field cannot completely separate it within 5 minutes, resulting in a turbid dispersion and slow separation. At 45°C, emulsifier F-3 particles agglomerate in the upper layer of the water. From the 4th minute onward, the dispersion becomes clear, and within 5 minutes, the emulsifier F-3 nanoparticles are almost completely separated, demonstrating a rapid separation rate. In summary, Fe₃O₄@SiO₂@PNIPAM exhibits excellent magnetocaloric responsiveness, and the grafting of PNIPAM chains increases the thermal separation efficiency of the emulsifier above the LSCT, offering advantages for reuse and energy conservation.

[0163] The experimental results show that in addition to the significant influence of Fe3O4@SiO2@PNIPAM particle concentration on the emulsification performance, F-3 aqueous solutions with concentrations of 0.01wt%, 0.1wt% and 0.5wt% were emulsified with toluene at an oil-water ratio of 5:5 at room temperature. The 0.01wt% sample had almost no emulsion formed due to its low concentration, and no droplets were observed. When the concentrations were 0.1wt% and 0.5wt%, the emulsion immediately showed stratification after emulsification. Figure 14 As can be seen, the emulsion with an F-3 concentration of 0.01wt% had the highest dehydration rate and the fastest dehydration speed. The emulsions with concentrations of 0.1wt% and 0.5wt% had similar dehydration rates (approximately 65%) in the first 6 hours, but after 6 hours, the dehydration rate of the 0.1wt% emulsion remained almost unchanged. The final dehydration rate of the 0.1wt% emulsion was 65%, and the dehydration rate of the 0.5wt% emulsifier continued to rise, ultimately reaching 95%. Clearly, the 0.1wt% concentration of emulsifier F-3 achieved the best emulsification effect. It should be noted that the lower the dehydration rate, the better the emulsification effect.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a magnetothermal dual-responsive green nanoemulsifier, characterized in that: The preparation method comprises the following steps: S1. A mixture of ferric salt and ferrous salt is dissolved in water, reacted in a N2 atmosphere under alkaline conditions to obtain Fe3O4 nanoparticles; S2. The Fe3O4 nanoparticles are dispersed in a first solvent, a basic catalyst, an organosilicon compound is added, and the reaction is carried out at room temperature until the system changes from black to dark gray to obtain Fe3O4@SiO2 nanoparticles; S3. After the Fe3O4@SiO2 nanoparticles are pretreated, they are dispersed in a second solvent, a first acid binding agent and an aminosilane solution are added, and after a first reaction, Fe3O4@SiO2@NH2 nanoparticles are obtained; the aminosilane solution is obtained by mixing aminosilane and water in a volume ratio of 3:5; S4. The Fe3O4@SiO2@NH2 nanoparticles are dispersed in an organic solvent, a second acid binding agent and an initiator are added, and the second reaction is performed to obtain Fe3O4@SiO2@Br nanoparticles; S5. Dispersing Fe3O4@SiO2@Br nanoparticles and polymerized monomers in water to obtain a first mixed solution; dissolving CuBr2 and L-ascorbic acid in water, and adding an organic ligand to obtain a second mixed solution; and under nitrogen protection, mixing the first mixed solution and the second mixed solution, and undergoing a third reaction, obtaining Fe3O4@SiO2@PNIPAM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier.

2. The preparation method according to claim 1, characterized in that In step S1: A mixture of ferric salt and ferrous salt is dissolved in water, and under a nitrogen atmosphere, an alkaline solution is added to a pH of 9.5-10, and the mixture is reacted at 65-70°C until black particles appear to obtain Fe3O4 nanoparticles.

3. The preparation method according to claim 2, characterized in that The molar ratio of the iron element in the ferric salt and the ferrous salt is 2:

1.

4. The preparation method according to claim 1, characterized in that In step S2: The dosage ratio of the Fe3O4 nanoparticles, the alkaline catalyst, and the organosilicon compound is (0.5-0.6) g: (2-3) mL: (1.5-2) mL; The first solvent is a mixture of anhydrous ethanol and water; the alkaline catalyst is ammonia water with a mass fraction of 20-28%; and / or The organic silicon compound is ethyl orthosilicate.

5. The preparation method according to claim 4, characterized in that The volume ratio of anhydrous ethanol to water in the first solvent is 3:

1.

6. The preparation method according to claim 1, wherein: In step S3, the Fe3O4@SiO2 nanoparticles are pretreated and then dispersed in a second solvent. A first acid binding agent and an aminosilane solution are added, the pH is adjusted to 8-10, and the mixture is reacted at 65-70°C for 4-12 hours to obtain Fe3O4@SiO2@NH2 nanoparticles. In step S4, the Fe3O4@SiO2@NH2 nanoparticles are dispersed in an organic solvent, a second acid binding agent is added, and the mixture is stirred in an ice-water bath at 4-6°C for 10-20 minutes. An initiator is added, and the mixture is reacted at 0-6°C for 1-2 hours and then at room temperature for 4-12 hours to obtain Fe3O4@SiO2@Br nanoparticles; and / or In step S5, under N2 protection, the first mixed solution and the second mixed solution are mixed and reacted at room temperature for 3 to 7 hours to obtain Fe3O4@SiO2@PNIPAM nanoparticles, which are the magnetothermal dual-responsive green nanoemulsifier.

7. The preparation method according to claim 1 or 6, characterized in that: In step S3, the pretreatment is to soak the Fe3O4@SiO2 nanoparticles in piranha solution for 10 to 20 minutes; The piranha solution is obtained by mixing a hydrogen peroxide solution and concentrated sulfuric acid in a volume ratio of 1:3; the mass fraction of the hydrogen peroxide solution is 30%.

8. The preparation method according to claim 1 or 6, characterized in that: In step S3, the dosage ratio of the Fe3O4@SiO2 nanoparticles, the first acid binding agent, and the aminosilane is (0.5-0.6) g: (0.05-0.06) mL: (0.3-0.45) mL; In step S4, the amount ratio of the Fe3O4@SiO2@NH2 nanoparticles, the second acid binding agent, and the initiator is (0.5-0.6) g: (0.3-0.4) mL: (0.2-0.3) mL; and / or In step S5, the mass ratio of the Fe3O4@SiO2@Br nanoparticles, the polymerization monomer, CuBr2, L-ascorbic acid, and the organic ligand is 0.2:(0.7~3):(0.05~0.07):(0.015~0.020):(0.13~0.15).

9. The preparation method according to claim 1 or 6, characterized in that In step S3: The second solvent is anhydrous ethanol; The first acid binding agent is triethanolamine or triethylamine; and / or The aminosilane is 3-aminopropyltriethoxysilane.

10. The preparation method according to claim 1 or 6, characterized in that: In step S4: The organic solvent is toluene; the second acid binding agent is pyridine; and / or The initiator is 2-bromoisobutyl bromide and / or 2-bromo-2-methylpropionyl bromide.

11. The preparation method according to claim 1 or 6, characterized in that: In step S5: The polymerizable monomer is N-isopropylacrylamide; and / or The organic ligand is one or more of tris(2-dimethylaminoethyl)amine, tris(2-aminoethyl)amine, and pentamethyldiethylenetriamine.

12. A magnetic-thermal dual-responsive green nanoemulsifier, characterized in that: The preparation method is described in any one of claims 1 to 11.

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