Nanometer core-shell particle, preparation method and application thereof

Abstract

The present application relates to the field of nanometer core-shell particles and its preparation, and in particular to a kind of nanometer core-shell particles and its preparation method and application, including the nanoparticle core containing metal elements, the shell layer containing metal elements, the polyhydroxy compound connecting the nanoparticle core and shell layer.The nanometer core-shell particle preparation method of the present application is simple to operate, and the functional combination of the nanoparticle core containing metal elements and the shell layer containing metal elements can be obtained by using the complexation between polyhydroxy compound and metal, so as to obtain functional nanoparticles meeting different application fields, which is expected to be applied in the fields of optics, electricity, chemistry, coating, detection, anti-counterfeiting and biomedicine.

Description

Technical Field

[0001] This invention relates to the field of core-shell nanoparticles and their preparation, specifically to a core-shell nanoparticle, its preparation method, and its application. Background Technology

[0002] With the continuous development of nanoscience and technology, people's requirements for nanomaterials in terms of preparation, properties, and applications are increasing, giving rise to the research and development of composite materials. Core-shell nanoparticles are a type of composite material with a central nanoparticle as the core and other elements as the outer shell, which is modified to achieve breakthroughs in performance.

[0003] Core-shell nanoparticles can be classified into three types based on their composition: organic-organic, inorganic-organic, and inorganic-inorganic. Metallic and compound inorganic particles possess excellent physical properties such as rigidity, thermal stability, magnetism, electrical conductivity, thermal conductivity, and wave absorption, as well as specific chemical properties such as catalytic activity and chemical color development. These properties have led to their widespread research in numerous application fields, including optics, electronics, chemistry, coatings, detection, anti-counterfeiting, and biomedicine. The preparation of metallic elemental, alloy, and compound core-shell nanoparticles typically requires satisfying lattice matching and directional bonding at the interface. Matching the lattice parameters of the core and shell materials can reduce shell growth stress and achieve epitaxial growth of the shell. However, the limited number of materials that meet the required lattice matching limits the types of core-shell nanoparticles that can be prepared. Currently, modification methods for achieving directional growth at the shell material interface through specific surface modifications have limited application conditions; therefore, the controllable synthesis of core-shell nanoparticles remains a challenge. Summary of the Invention

[0004] To overcome the above technical problems, this invention provides a nano-core-shell particle, its preparation method and application. A polyhydroxy compound is introduced as a transition layer on the surface of the core nanoparticle to alleviate lattice mismatch. Furthermore, by utilizing the strong coordination complexation between the polyhydroxy compound and the metal, a shell containing metal elements is stably and controllably coated on the core surface of the core nanoparticle, thus synthesizing the nano-core-shell particle.

[0005] One of the objectives of this invention is to provide a nano-core-shell particle, which is formed by the partial hydroxyl bonds of a polyhydroxy compound complexing with the core of a nanoparticle containing a metal element, and the partial hydroxyl bonds complexing with metal ions in the shell containing a metal element.

[0006] The second objective of this invention is to provide a method for preparing core-shell nanoparticles. This method utilizes the principle that hydroxyl groups in polyhydroxy compounds can form stable coordination bonds with metal ions. Sufficient polyhydroxy compounds are modified on the surface of nanoparticle cores containing metal elements. The nanoparticle cores are then used as seeds to coat their surfaces with a shell containing metal elements, thereby synthesizing core-shell nanoparticles.

[0007] The third objective of this invention is to provide an application of nano-core-shell particles.

[0008] The fourth objective of this invention is to provide another application of core-shell nanoparticles.

[0009] To achieve one of its objectives, the present invention employs the following technical solution: a nano-core-shell particle comprising a nanoparticle core containing a metal element, a shell containing a metal element, and a polyhydroxy compound connecting the nanoparticle core and the shell.

[0010] Preferably, the nanoparticle core comprises at least one element, alloy, oxide, or sulfide of iron, cobalt, nickel, copper, zinc, cerium, cadmium, aluminum, molybdenum, vanadium, manganese, chromium, tin, europium, gadolinium, zirconium, rhodium, tungsten, terbium, titanium, germanium, indium, gold, silver, platinum, ruthenium, and palladium; the shell comprises at least one element, alloy, oxide, or sulfide of iron, cobalt, nickel, copper, zinc, cerium, cadmium, aluminum, molybdenum, vanadium, manganese, chromium, tin, europium, gadolinium, zirconium, rhodium, tungsten, terbium, titanium, germanium, indium, gold, silver, platinum, ruthenium, and palladium; the nanoparticle core and the shell have different material compositions.

[0011] Preferably, the alloy comprises a binary, ternary, or multi-element alloy of at least one of the following substances: iron, cobalt, nickel, copper, zinc, cerium, cadmium, aluminum, molybdenum, vanadium, manganese, chromium, tin, zirconium, rhodium, tungsten, titanium, germanium, indium, gold, silver, platinum, ruthenium, and palladium; the oxide comprises at least one of the following: iron(II,III) oxide, ferric oxide, ferric cobaltate, nickel cobaltate, nickel oxide, cuprous oxide, copper oxide, zinc oxide, cerium oxide, cadmium oxide, aluminum oxide, manganese oxide, chromium oxide, tin oxide, zirconium dioxide, tungsten oxide, titanium dioxide, and indium oxide; and the sulfide comprises at least one of the following: ferrous sulfide, cobalt sulfide, nickel sulfide, copper sulfide, zinc sulfide, cadmium sulfide, molybdenum sulfide, vanadium sulfide, manganese sulfide, tin sulfide, tungsten sulfide, indium sulfide, and silver sulfide.

[0012] The metal-containing shell can coordinate and complex with polyhydroxy compounds, allowing them to grow and coat the surface of the metal-containing nanoparticle core.

[0013] Preferably, the average particle size of the nanoparticle core is 5-500 nm.

[0014] Preferably, the average thickness of the shell is 5-400 nm.

[0015] Preferably, the polyhydroxy compound is a polyphenolic compound, including flavonoids, flavonols, catechins, phenolic acids, lignans, tannins, anthocyanins, etc., specifically at least one of apigenin, kaempferol, epicatechin, epigallocatechin, epigallocatechin gallate, gallic acid, enterodiol, tannic acid, proanthocyanidins, cyanidin-3-O-glucoside, and pyrogallol.

[0016] To achieve the second objective of this invention, the following technical solution is adopted: a method for preparing the aforementioned core-shell nanoparticles, comprising the following steps:

[0017] (1) Preparation of nanoparticle cores containing metal elements with surface-coordinated complexation modified polyhydroxy compounds;

[0018] (2) Prepare a precursor solution for synthesizing a shell containing metal elements, mix the prepared nanoparticles with the precursor solution, and coat the nanoparticle core with the shell at the reaction temperature to obtain the nano core-shell particles.

[0019] In this invention, the principle that the hydroxyl groups in polyhydroxy compounds can form stable coordination bonds with metal ions is utilized. Sufficient polyhydroxy compounds are modified on the surface of nanoparticle cores containing metal elements. The polyhydroxy compounds are used as nucleation growth sites for the shell containing metal elements on the surface of the nanoparticle cores to synthesize the shell on the surface of the nanoparticle cores.

[0020] The core of the preparation method of the present invention lies in the fact that the lone pair of electrons contained in the oxygen atom of the hydroxyl group of the polyhydroxy compound can act as a coordinating atom to form a non-selective strong coordination complex with the metal ion, and modify it on the core surface of the nanoparticle containing the metal element, so as to provide sufficient and uniform nucleation growth sites for the shell material containing the metal element, and thus the shell material coats the surface of the nanoparticle core, thereby obtaining nano core-shell particles.

[0021] Preferably, when the nanoparticle core is modified by coordination complexation with the polyhydroxy compound, the concentration of the polyhydroxy compound in the solution is between 0.1 mg / ml and saturation concentration; the solution for coordination complexation includes any liquid capable of dissolving the polyhydroxy compound, including but not limited to one or more of carbonates, carboxylic esters, ethers, alkanols, acetonitrile, dimethyl sulfoxide, pure water, acetone, and sodium salt buffer solutions; the carbonate includes at least one of propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; the carboxylic ester includes at least one of γ-butyrolactone, ethyl acetate, and methyl formate; the ether includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxymethane, and 1,2-dimethoxyethane.

[0022] Preferably, in step (1), the method for preparing the nanoparticle core of the surface coordination complex modified with polyhydroxy compound includes any one of the following: A. preparing a polyhydroxy compound solution, then adding a nanoparticle core containing a metal element and mixing evenly; B. preparing a nanoparticle core solution containing a metal element, then adding a polyhydroxy compound and mixing evenly; C. preparing a polyhydroxy compound solution and a nanoparticle core solution containing a metal element respectively, then mixing the two solutions evenly; D. directly adding nanoparticles containing a metal element and a polyhydroxy compound to the solution and mixing evenly.

[0023] Preferably, in step (2), the precursor liquid includes a metal source, an additive and a solvent; or a metal source, a sulfur source, an additive and a solvent.

[0024] The precursor solution for synthesizing a shell containing metal elements includes raw materials, auxiliaries, and solvents for synthesizing a shell containing metal elements. A nanoparticle core containing metal elements modified with a polyhydroxy compound is added to the precursor solution, and the experimental parameters are adjusted to carry out the coating reaction. After the reaction is completed, the reaction solvent is removed by washing with pure water and ethanol to obtain nanocore-shell particles.

[0025] Preferably, the metal source is a soluble salt of a metal, and the sulfur source is at least one selected from sodium sulfide, ammonium sulfide, thioacetamide, and thiourea. In the precursor solution, the mass fraction of the metal source is 0.05%-10%, and the mass fraction of the sulfur source is 0.01%-5%.

[0026] Preferably, the soluble salt of the metal includes at least one of the following: metal nitrate, chloride, acetate, sulfate, metal acetylacetonate, etc.

[0027] Preferably, the solvent is a solution capable of dissolving the metal source or the metal source and sulfur source and dispersant, including but not limited to pure water, dimethylformamide, octadecene, octadecylamine, toluene, and at least one of alcohols, including at least one of methanol, ethanol, ethylene glycol, diethylene glycol, butanol, butanediol, isopropanol, benzyl alcohol, and polyethylene glycol.

[0028] Preferably, the additive includes a dispersant, which is at least one of anionic surfactants, cationic surfactants, and nonionic surfactants. The anionic surfactant includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium citrate, sodium oleate, oleic acid, ethylenediaminetetraacetic acid, and thioacetic acid. The cationic surfactant includes at least one of dodecyltrimethylammonium bromide, didodecyldimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride. The nonionic surfactant includes at least one of polyvinylpyrrolidone, polyethylene glycol, and oleylamine. In the precursor solution, the mass fraction of the dispersant is 0.05%-10%.

[0029] Preferably, the auxiliary agent may further include an acid-base regulator. In the partial synthesis, the reaction rate can be adjusted by adding an acid-base regulator. The acid-base regulator is one or more of sodium hydroxide, potassium hydroxide, sodium acetate, ammonia, urea, and ethylenediamine, and the mass fraction of the acid-base regulator is 0-10%.

[0030] Preferably, the auxiliary agent may further include a reducing agent, which is added in part of the synthesis to promote the synthesis of the target product. The reducing agent is one or more of ethylene glycol, ascorbic acid, sodium citrate, glucose, sodium borohydride, and oleylamine, and the mass fraction of the reducing agent is 0-10%.

[0031] To achieve the third objective, the present invention adopts the following technical solution: an application of the aforementioned core-shell nanoparticles, applying the core-shell nanoparticles to the fields of optics, electronics, chemistry, coatings, detection, anti-counterfeiting, or biomedicine.

[0032] To achieve its fourth objective, this invention employs the following technical solution: The nano-core-shell particles prepared by the above method are applied to the field of photonic crystals. Specifically, light-colored monodisperse magnetic nano-core-shell particles are obtained by coating the surface of black monodisperse magnetic nanoparticles with a light-colored shell containing metal elements. This light-colored shell reduces the high absorption loss caused by the non-selective absorption of incident light by the chemical color of the magnetic nanoparticles, thereby increasing the structural color reflection intensity of the photonic crystal.

[0033] The mechanism by which the chemical color of light-colored magnetic core-shell nanoparticles enhances the structural color is as follows: When these particles assemble into structural colors under the influence of an electric and / or magnetic field, their absorption and reflection of light differs across wavelengths. When the chemical and structural color wavelengths separate, the light in the structural color band may be absorbed or weakened by the material itself, leading to a decrease in structural color intensity. Conversely, when the chemical and structural color wavelengths overlap, the material's absorption of light in the non-reflective bands enhances color purity, making the structural color more pronounced. By controlling the synthesis time, the shell thickness can be controlled, resulting in magnetic core-shell nanoparticles with chemical colors ranging from dark to light. This adjusts the absorption of visible light by the structural units, achieving synergistic color development of both chemical and structural colors and ultimately increasing the brightness of the structural color.

[0034] The beneficial effects of this invention are as follows:

[0035] (1) This invention provides a simple and universal method for synthesizing nano-core-shell particles by using the complexation between polyhydroxy compounds and metals to achieve the coating of shell material on the surface of core material, thereby preparing nano-core-shell particles.

[0036] (2) The nano-core-shell particles prepared by the present invention combine metals and their compounds with different functions to obtain dual properties, thus expanding their application fields.

[0037] (3) The nano-core-shell particles prepared by this invention can be applied to the field of photonic crystals to improve the brightness of structural colors. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the nano-core-shell particles of the present invention;

[0039] Figure 2 Magneto-responsive photonic crystal chemical color digital images of uncoated Fe3O4 nanoparticles (a) and Fe3O4@CeO2 core-shell nanoparticles prepared in Examples 1-5 (b)-(f);

[0040] Figure 3 The graph shows the relationship between the shell thickness of uncoated Fe3O4 and the Fe3O4@CeO2 core-shell nanoparticles prepared in Examples 1-5 and the high chemical color brightness.

[0041] Figure 4 SEM images of uncoated Fe3O4 nanoparticles (a) and Fe3O4@CeO2 core-shell nanoparticles prepared in Examples 1-5 (b)-(f);

[0042] Figure 5 The reflection spectra of Fe3O4@CeO2 photonic crystal (a) and Fe3O4 photonic crystal (b) with the same particle size prepared in Example 1 under a magnetic field;

[0043] Figure 6 The reflection spectra of Fe3O4@CeO2 photonic crystal (a) and Fe3O4 photonic crystal (b) with the same particle size prepared in Example 2 under a magnetic field;

[0044] Figure 7 The reflection spectra of Fe3O4@CeO2 photonic crystal (a) and Fe3O4 photonic crystal (b) with the same particle size prepared in Example 3 under a magnetic field;

[0045] Figure 8 The reflection spectra of Fe3O4@CeO2 photonic crystal (a) and Fe3O4 photonic crystal (b) with the same particle size prepared in Example 4 under a magnetic field;

[0046] Figure 9 The reflection spectra of Fe3O4@CeO2 photonic crystal (a) and Fe3O4 photonic crystal (b) prepared in Example 5 under a magnetic field;

[0047] Figure 10SEM images of uncoated Fe3O4 nanoparticles (a) and Fe3O4@CeO2 core-shell nanoparticles prepared in Example 6 (b);

[0048] Figure 11 The reflection spectrum of the Fe3O4@CeO2 photonic crystal prepared in Example 6 under a magnetic field;

[0049] Figure 12 The reflection spectrum of the Fe3O4@CeO2 photonic crystal prepared in Example 6 under an electric field;

[0050] Figure 13 SEM images of Fe3O4 nanoparticles (a) and Fe3O4@CeO2 core-shell nanoparticles prepared in Example 7 (b);

[0051] Figure 14 The reflection spectrum of the Fe3O4@CeO2 photonic crystal prepared in Example 7 under a magnetic field;

[0052] Figure 15 SEM images of uncoated Fe3O4 nanoparticles (a) and Fe3O4@CeO2 core-shell nanoparticles prepared in Example 9 (b);

[0053] Figure 16 SEM images of uncoated Fe3O4 nanoparticles (a) and Fe3O4@ZnS core-shell nanoparticles prepared in Example 12 (b). Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0055] This invention provides a nano-core-shell particle, the structure of which is shown below. Figure 1 In this embodiment of the invention, the nanocore-shell particle includes: a nanoparticle core containing a metal element, a shell containing a metal element, and a polyhydroxy compound connecting the nanoparticle core and the shell.

[0056] In the technical solution of this invention, the surface of the nanoparticle core containing the metal element can be linked to a polyhydroxy compound through a complexation process; some hydroxyl bonds of the polyhydroxy compound complex with the nanoparticle core containing the metal element, and some hydroxyl bonds complex with the shell layer containing the metal element. Thus, after modifying the surface of the nanoparticle core containing the metal element with a layer of polyhydroxy compound, the uncomplexed hydroxyl bonds can serve as nucleation sites for the shell layer containing the metal element, thereby synthesizing core-shell nanoparticles. It is understood that the technical solution of this invention enables controllable coating of the shell layer containing the metal element.

[0057] In this invention, the average particle size of the nanoparticle core is 5-500 nm.

[0058] In this invention, the polyhydroxy compound is a polyphenolic compound, including flavonoids, flavonols, catechins, phenolic acids, lignans, tannins, anthocyanins, etc. Specifically, it may be at least one of apigenin, kaempferol, epicatechin, epigallocatechin, epigallocatechin gallate, gallic acid, enterodiol, tannic acid, proanthocyanidins, cyanidin-3-O-glucoside, and pyrogallol.

[0059] In this invention, the average thickness of the shell layer is 5-400 nm.

[0060] In this invention, the nanoparticle core material is selected from at least one element, alloy, oxide, or sulfide of iron, cobalt, nickel, copper, zinc, cerium, cadmium, aluminum, molybdenum, vanadium, manganese, chromium, tin, europium, gadolinium, zirconium, rhodium, tungsten, terbium, titanium, germanium, indium, gold, silver, platinum, ruthenium, and palladium; the shell material is selected from at least one element, alloy, oxide, or sulfide of iron, cobalt, nickel, copper, zinc, cerium, cadmium, aluminum, molybdenum, vanadium, manganese, chromium, tin, europium, gadolinium, zirconium, rhodium, tungsten, terbium, titanium, germanium, indium, gold, silver, platinum, ruthenium, and palladium; the nanoparticle core and shell have different material compositions.

[0061] This invention provides a method for preparing core-shell nanoparticles. The core-shell nanoparticles are characterized as described above, but are primarily characterized by utilizing the principle that hydroxyl groups in polyhydroxy compounds can form stable coordination bonds with metal ions. A sufficient amount of polyhydroxy compound is modified onto the surface of a metal-containing nanoparticle core. The polyhydroxy compound serves as a nucleation and growth site for the metal-containing shell on the nanoparticle core surface, thus coating the nanoparticle core with a shell. Specifically, the method includes the following steps:

[0062] (1) Preparation of nanoparticle cores containing metal elements with surface-coordinated complexation modified polyhydroxy compounds;

[0063] (2) A precursor solution containing a metal element was prepared. The precursor solution included raw materials, additives, and solvent. A metal element-containing nanoparticle core modified with a polyhydroxy compound was added to the precursor solution. The experimental parameters were adjusted to carry out the coating reaction. After the reaction was completed, the reaction solvent was removed by washing with pure water and ethanol to obtain the core-shell nanoparticles.

[0064] It should be noted that, in the embodiments of the present invention, the method for preparing the metal-containing nanoparticle core of the surface-coordinated complex modified polyhydroxy compound includes any one of the following: A. preparing a polyhydroxy compound solution, then adding the metal-containing nanoparticle core, and mixing evenly; B. preparing a metal-containing nanoparticle core solution, then adding the polyhydroxy compound and mixing evenly; C. preparing a polyhydroxy compound solution and a metal-containing nanoparticle core solution separately, then mixing the two solutions evenly; D. directly adding the metal-containing nanoparticles and the polyhydroxy compound to the solution and mixing evenly.

[0065] The method for preparing the polyhydroxy compound solution is as follows: Weigh the polyhydroxy compound, dissolve it in the solution, and obtain the polyhydroxy compound solution.

[0066] Preparation method of nanoparticle solution containing metal element: Weigh nanoparticles containing metal element, disperse them in solution to obtain nanoparticles containing metal element.

[0067] Nanoparticle cores are coordinated and complexed with polyhydroxy compounds for modification. The concentration of polyhydroxy compounds in the solution during modification is between 0.1 mg / ml and saturation concentration.

[0068] The solution for coordination complexation is any liquid capable of dissolving polyhydroxy compounds, including but not limited to one or more of carbonates, carboxylic esters, ethers, alkanols, acetonitrile, dimethyl sulfoxide, pure water, acetone, and sodium salt buffer solutions; the carbonates include at least one of propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; the carboxylic esters include at least one of γ-butyrolactone, ethyl acetate, and methyl formate; the ethers include at least one of tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxymethane, and 1,2-dimethoxyethane.

[0069] In this embodiment of the invention, the shell material containing metal elements is a synthetic material composed of at least one element, alloy, oxide, or sulfide from the following: iron, cobalt, nickel, copper, zinc, cerium, cadmium, aluminum, molybdenum, vanadium, manganese, chromium, tin, europium, gadolinium, zirconium, rhodium, tungsten, terbium, titanium, germanium, indium, gold, silver, platinum, ruthenium, and palladium that is not the same as the core component of the nanoparticles.

[0070] The raw materials for the metal element include at least one of metal nitrates, metal chlorides, metal acetates, metal sulfates, and metal acetylacetonates, with a mass percentage of 0.05%-10% for the metal source; the raw materials for the sulfur element include at least one of sodium sulfide, ammonium sulfide, thioacetamide, and thiourea (TU), with a mass percentage of 0.01%-10% for the sulfur source.

[0071] In this embodiment of the invention, the auxiliary agent includes a dispersant. The dispersant is used to prevent agglomeration during the synthesis process and to stabilize the dispersion. It includes at least one of anionic surfactants, cationic surfactants, and nonionic surfactants. The anionic surfactants include at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium citrate, sodium oleate, oleic acid, ethylenediaminetetraacetic acid, and thioglycolic acid. The cationic surfactants include at least one of dodecyltrimethylammonium bromide, didodecyldimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride. The nonionic surfactants include at least one of polyvinylpyrrolidone, polyethylene glycol, and oleylamine. In the precursor solution, the mass percentage of the dispersant is 0.05%-10%.

[0072] In this embodiment of the invention, the solvent is a solution capable of dissolving the aforementioned metal source or metal source and sulfur source and dispersant, including but not limited to pure water, dimethylformamide, octadecene, octadecylamine, toluene, and at least one of alcohols, including at least one of methanol, ethanol, ethylene glycol, diethylene glycol, butanol, butanediol, isopropanol, benzyl alcohol, and polyethylene glycol.

[0073] In this embodiment of the invention, the auxiliary agent for the synthesis of the shell containing some metal elements also includes an acid-base regulator, which is one or more of sodium hydroxide, potassium hydroxide, sodium acetate, ammonia, urea, and ethylenediamine, and the mass fraction of the acid-base regulator is 0-10%.

[0074] In this embodiment, the auxiliary agent for the synthesis of the shell containing metal elements also includes a reducing agent, which includes one or more of ethylene glycol, ascorbic acid, sodium citrate, glucose, sodium borohydride, and oleylamine, with a mass fraction of 0-10%.

[0075] In this embodiment of the invention, the dissolution method includes ultrasonication, magnetic stirring, and heating stirring.

[0076] In this embodiment of the invention, the experimental parameters in the step of "adjusting experimental parameters to carry out the coating reaction" include reaction temperature, reaction time, and number of reactions. The coating reaction temperature is from room temperature to 300°C. oC, can be determined based on the reaction temperature of the synthesized shell containing metal elements. This is existing technology, and those skilled in the art can select a suitable reaction temperature as needed. The coating reaction time is 0.5-24 hours; the coating reaction is repeated at least once. By adjusting the above reaction parameters, the shell thickness can be controlled within the range of 5-500 nm. This invention is not limited to this; any method for preparing nano-core-shell particles of a specific size by adjusting the above parameters is within the scope of protection of this invention.

[0077] The method for preparing the magnetically responsive photonic crystal according to CN117550651A in this embodiment of the invention is as follows: the monodisperse nanocore-shell particles prepared above are dispersed in an organic solvent or a solvent containing a dispersant, and ultrasonically dispersed until uniform to obtain the magnetically responsive photonic crystal. The dispersant is a general-purpose dispersant, including common ionic and nonionic dispersants, whose function is to reduce the surface tension of the nanoparticles in the solvent, prevent aggregation, and provide the repulsive force required for photonic crystal assembly. The solvent includes at least one of alcohols, alcohol ethers, halogenated hydrocarbons, γ-butyrolactone, ethyl lactate, dimethyl sulfoxide, and dimethylformamide. Alcohols include at least one of ethylene glycol, butanol, 1,4-butanediol, 1,3-butanediol, and glycerol; alcohol ethers include at least one of ethylene glycol ether, diethylene glycol, triethylene glycol, hexamethylene glycol, polyethylene glycol 400, diethylene glycol butyl ether, and ethylene glycol butyl ether; halogenated hydrocarbons include at least one of dichloromethane, dichloroethane, and chloroform.

[0078] In this embodiment of the invention, the electroresponsive photonic crystal is prepared according to the preparation method described in CN117608010A.

[0079] The present invention will be further illustrated by specific embodiments below. The specific embodiments provided herein are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0080] Example 1

[0081] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0082] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0083] S1. Preparation of Fe3O4@tannic acid nanoparticles: 130nm Fe3O4 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and then centrifuged to obtain tannic acid modified Fe3O4 particles (Fe3O4@TA).

[0084] Synthesis of S2.Fe3O4@CeO2 core-shell nanoparticles: 4g Ce(NO3)3·6H2O, 7g PVP, and 98ml ethylene glycol solution were mixed and placed at 75°C. o Stir at C for 30 min until all reactants are dispersed in the solvent. Then add 120 mg of Fe3O4@tannic acid particles dispersed in 2 ml of ethylene glycol. Heat to 155 °C. o At C, the reaction was carried out for 1 hour for the first coating. After the reaction, the nanoparticles were washed with pure water and ethanol to obtain Fe3O4@CeO2 nanoparticles with CeO2 primary crystal grains on the surface. 4g of Ce(NO3)3·6H2O, 7g of PVP, and 98ml of ethylene glycol solution were mixed and placed at 75°C. o Stir at temperature C for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of ethylene glycol solution containing Fe3O4@CeO2 nanoparticles with primary CeO2 crystals, and heat to 155 °C. o C, react for 45 min, then perform a second coating. After the reaction is complete, wash with pure water and ethanol to obtain Fe3O4@CeO2 magnetic core-shell nanoparticles with a uniform CeO2 shell on the surface.

[0085] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0086] Figure 2 In the images (a) and (b), respectively, are the magnetoresponsive photonic crystal chemichromatic digital images of Fe3O4 and Fe3O4@CeO2 nanocore-shell particles prepared in Example 1. It can be observed that the solution color changes from grayish-black to dark brown after coating. From... Figure 3 As can be seen from this, the chemical color of the photonic crystal prepared in this embodiment is 5.3 times brighter than that of the Fe3O4 photonic crystal. Figure 4 (a) and (b) are SEM images of Fe3O4 nanoparticles and Fe3O4@CeO2 core-shell nanoparticles prepared in Example 1, respectively. It can be seen that the coating process did not lead to agglomeration between nanoparticles. The core-shell nanoparticles are uniform spherical and have good monodispersity. The shell thickness after coating is relatively uniform. The average particle size of Fe3O4@CeO2 core-shell nanoparticles is 140 nm, and the CeO2 shell thickness is about 5 nm. Figure 5 (a) shows the reflection spectra of the Fe3O4@CeO2 photonic crystal prepared in Example 1 and (b) shows the reflection spectra of Fe3O4 photonic crystals with the same particle size under a magnetic field. Figure 5Spectroscopic data showed that the Fe3O4@CeO2 nanoparticles synthesized under the conditions described in Example 1 had increased chemical color reflectance compared to Fe3O4. The peak shift distances of the two photonic crystals under a magnetic field were similar. Under the same peak position conditions, the structural color reflectance of Fe3O4@CeO2 was about three times that of Fe3O4. This is attributed to the increase in the chemical color of the particles, which reduced the light absorption loss and the more regular structure brought about by PVP-assisted assembly in the solution.

[0087] Example 2

[0088] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0089] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 1, except that the second coating reaction time is 1 hour.

[0090] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0091] Figure 2 Image (c) shows the chemical colorimetric image of the magnetoresponsive photonic crystal of the Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment; the solution color changes to light brown. From Figure 3 As can be seen, the chemical color of the photonic crystal prepared in this embodiment is 9.7 times brighter than that of the Fe3O4 photonic crystal. Figure 4 Image (c) is a SEM image of the Fe3O4@CeO2 nanocore-shell particles prepared in this embodiment. It can be seen that the Fe3O4@CeO2 nanocore-shell particles have good monodispersity, the CeO2 shell layer is uniformly thickened, the average particle size of the Fe3O4@CeO2 nanocore-shell particles is 151 nm, and the CeO2 shell layer thickness is about 10.5 nm. Figure 6 (a) shows the reflection spectra of the Fe3O4@CeO2 photonic crystal prepared in Example 2 and (b) shows the reflection spectra of the Fe3O4 photonic crystal under a magnetic field. Figure 6 The spectral data showed that the Fe3O4@CeO2 photonic crystal synthesized under the conditions described in Example 2 had an increased chemical color reflectance compared to Fe3O4, and its structural color reflectance was about six times that of the Fe3O4 photonic crystal. Compared to the Fe3O4 photonic crystal prepared in Example 1, the structural color reflection peak showed a red shift, and the structural color reflectance increased. This is attributed to the increased shell thickness and the increased chemical color of the particles, which reduced the light absorption loss.

[0092] Example 3

[0093] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0094] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 1, except that the second coating reaction time is 1.5 h.

[0095] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0096] Figure 2 Image (d) shows the magnetochromatic digital image of the Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment, revealing that the solution color continues to lighten. From... Figure 3 As can be seen from this, the chemical color of the photonic crystal prepared in this embodiment is 19.1 times brighter than that of the Fe3O4 photonic crystal. Figure 4 Image (d) shows the SEM image of the Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment. It can be seen that the Fe3O4@CeO2 core-shell nanoparticles have good monodispersity, uniform size and no agglomeration. The average particle size of the Fe3O4@CeO2 core-shell nanoparticles is 161 nm and the CeO2 shell thickness is about 15.5 nm. Figure 7 (a) shows the reflection spectra of the Fe3O4@CeO2 photonic crystal prepared in this embodiment and (b) shows the reflection spectra of the Fe3O4 photonic crystal under a magnetic field. Figure 7 Spectroscopic data showed that the Fe3O4@CeO2 nanoparticles synthesized under the conditions described in this embodiment had increased chemical color reflectance compared to Fe3O4, and approximately seven times the structural color reflectance of Fe3O4. Compared to the Fe3O4 photonic crystal prepared in Example 2, the structural color reflection peak showed a redshift, and the structural color reflectance increased. This is attributed to the increased shell thickness and the increased chemical color of the particles, which reduced light absorption loss.

[0097] Example 4

[0098] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0099] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 1, except that the second coating reaction time is 2 hours.

[0100] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0101] Figure 2 Image (e) shows the magnetochromatic digital image of the Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment, revealing that the solution color continues to lighten. From... Figure 3 It can be seen that the chemical color of the photonic crystal prepared in this embodiment is 29 nits brighter than that of the Fe3O4 photonic crystal. Figure 4 Image (e) is a SEM image of the Fe3O4@CeO2 nano-core-shell particles prepared in this embodiment. It can be seen that the Fe3O4@CeO2 nano-core-shell particles have good monodispersity, uniform size and no agglomeration. The average particle size of the Fe3O4@CeO2 nano-core-shell particles is 168 nm and the CeO2 shell thickness is about 19 nm. Figure 8 (a) shows the reflection spectra of the Fe3O4@CeO2 photonic crystal prepared in this embodiment and (b) shows the reflection spectra of the Fe3O4 photonic crystal under a magnetic field. Figure 8 Spectroscopic data revealed that the Fe3O4@CeO2 nanoparticles synthesized under the conditions described in this embodiment exhibited increased chemical color reflectance compared to Fe3O4, and significantly higher structural color reflectance than the Fe3O4 photonic crystal. Compared to the Fe3O4 photonic crystal prepared in Example 3, the structural color reflectance peak showed a redshift. This increase in structural color reflectance is attributed to the increased shell thickness and the enhanced chemical color of the particles, which reduced light absorption loss.

[0102] Example 5

[0103] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0104] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 1, except that the second coating reaction time is 2.5 h.

[0105] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0106] Figure 2 Image (f) shows the magnetochromatic digital image of the Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment, revealing that the solution color continues to lighten. From... Figure 5 As can be seen from this, the chemical color of the photonic crystal prepared in this embodiment is 32 nits brighter than that of the Fe3O4 photonic crystal. Figure 4Image (f) is a SEM image of the Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment. It can be seen that the Fe3O4@CeO2 core-shell nanoparticles have good monodispersity, uniform size and no agglomeration. The average particle size of the Fe3O4@CeO2 core-shell nanoparticles is 174 nm and the CeO2 shell thickness is about 22 nm. Figure 9 (a) shows the reflection spectra of the Fe3O4@CeO2 photonic crystal prepared in this embodiment and (b) shows the reflection spectra of the Fe3O4 photonic crystal under a magnetic field. Figure 9 Spectral data showed that the Fe3O4@CeO2 nanoparticles synthesized under the conditions described in this embodiment had increased chemical color reflectance compared to Fe3O4, and their structural color reflectance was significantly higher than that of the Fe3O4 photonic crystal. Compared to the Fe3O4 photonic crystal prepared in Example 4, the structural color reflection peak showed a redshift, indicating an increase in structural color reflectance. This is attributed to the increased shell thickness and the increased chemical color of the particles, which reduced light absorption loss.

[0107] Figure 2 , Figure 3 , Figure 4 The images show the magnetic response photonic crystal chemical color digital diagram, chemical color brightness relationship diagram, and scanning electron microscope image of Fe3O4 nanoparticles and Fe3O4@CeO2 core-shell nanoparticles prepared in Examples 1-5, respectively.

[0108] Figure 2 Image (a) shows the chemical color digital diagram of the Fe3O4 photonic crystal. Figure 2 In the middle (b)-(f), the magnetic response photonic crystal chemical color digital images of Fe3O4@CeO2 nano-core-shell particles prepared in Examples 1-5 are respectively. It can be seen intuitively that as the shell thickness of Fe3O4@CeO2 nano-core-shell particles increases, the chemical color of the nano-core-shell particles gradually changes from gray-black to light yellow. Figure 3 The graph shows the relationship between the shell thickness and chemical color brightness of uncoated Fe3O4 and Fe3O4@CeO2 nanocore-shell particles prepared in Examples 1-5. The chemical color brightness of Fe3O4 is 20.92. The chemical color of Fe3O4@CeO2 nanocore-shell particles increases stepwise with the increase of CeO2 shell thickness. Figure 4 This is a scanning electron microscope image of nanoparticles. Figure 4 Image (a) is a SEM image of Fe3O4 nanoparticles. Figure 4 Images (b)-(f) are SEM images of the Fe3O4@CeO2 core-shell nanoparticles prepared in Examples 1-5, respectively. The average particle size of the Fe3O4 nanoparticles is 130 nm, and the average particle size of the Fe3O4@CeO2 core-shell nanoparticles increases with increasing reaction time. Figure 2-4 As can be seen, extending the reaction time results in a lighter chemical color, and the brightness of the chemical color increases proportionally to the thickness of the shell.

[0109] Example 6

[0110] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0111] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 1, except that the particle size of the core nanoparticles is 95 nm and the second coating reaction time is 2 h.

[0112] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0113] The above-mentioned core-shell nanoparticles were used to prepare an electroresponsive photonic crystal according to the preparation method described in CN117608010A.

[0114] Figure 10 (a) shows the SEM images of Fe3O4 nanoparticles and (b) shows the Fe3O4@CeO2 core-shell nanoparticles prepared in this example. It can be seen that the nanoparticles are spherically uniform, have no agglomeration between particles, and have good monodispersity. Figure 11 This is the reflection spectrum of the Fe3O4@CeO2 photonic crystal prepared in this embodiment under a magnetic field, obtained by... Figure 11 Spectral data show that the Fe3O4@CeO2 photonic crystal prepared in this embodiment can be well assembled under a magnetic field, with the structural color reflection peak at around 550nm-650nm and a shift distance of about 100nm. Figure 12 This is the reflection spectrum of the Fe3O4@CeO2 photonic crystal prepared in this embodiment under an electric field. Figure 12 Spectral data show that the Fe3O4@CeO2 photonic crystal prepared in this embodiment has a good structural color reflection peak under an electric field, with the structural color reflection peak around 560nm-670nm and a shift distance of about 110nm.

[0115] Example 7

[0116] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0117] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 1, except that the particle size of the core nanoparticles is 155 nm and the second coating reaction time is 2 h.

[0118] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@CeO2 core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0119] Figure 13 (a) shows the SEM images of Fe3O4 nanoparticles and (b) shows the Fe3O4@CeO2 core-shell nanoparticles prepared in this example. It can be seen that the nanoparticles are spherically uniform, have no agglomeration between particles, and have good monodispersity. Figure 14 This is the reflection spectrum of the Fe3O4@CeO2 photonic crystal prepared in this embodiment under a magnetic field, obtained by... Figure 14 Spectral data show that the Fe3O4@CeO2 photonic crystal prepared in this embodiment can be well assembled under a magnetic field, with the structural color reflection peak around 655nm-820nm and a shift distance of about 165nm.

[0120] Example 8

[0121] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0122] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0123] S1. Preparation of Fe3O4@tannic acid nanoparticles: 130nm Fe3O4 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and then centrifuged to obtain tannic acid modified Fe3O4 particles (Fe3O4@TA).

[0124] Synthesis of S2.Fe3O4@CeO2 core-shell nanoparticles: 4g Ce(NO3)3·6H2O, 7g PVP, and 98ml ethylene glycol solution were mixed and placed at 75°C. o Stir at C for 30 min until all reactants are dispersed in the solvent. Then add 120 mg of Fe3O4@tannic acid particles dispersed in 2 ml of ethylene glycol. Heat to 155 °C. o C, react for 3 hours, wash with pure water and ethanol to obtain Fe3O4@CeO2 magnetic core-shell nanoparticles with a CeO2 shell on the surface.

[0125] Example 9

[0126] A type of nanocore-shell particle comprising Fe3O4 particles, epicatechin (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0127] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0128] S1. Preparation of Fe3O4@catechin nanoparticles: 130nm Fe3O4 particles and epicatechin were added to 5ml of ethanol at a mass ratio of 20:1. The mixture was ultrasonically complexed for 5min at room temperature and then centrifuged to obtain epicatechin-modified Fe3O4 particles (Fe3O4@epicatechin).

[0129] Synthesis of S2.Fe3O4@CeO2 core-shell nanoparticles: 4g Ce(NO3)3·6H2O, 7g PVP, and 98ml ethylene glycol solution were mixed and placed at 75°C. o Stir at C temperature for 30 min until all reactants are dispersed in the solvent, then add 120 mg of Fe3O4@epicatechin nanoparticles dispersed in 2 ml of ethylene glycol, and heat to 155 °C. o At C, the reaction was carried out for 1 hour, and the mixture was washed with pure water and ethanol to obtain Fe3O4@CeO2 nanoparticles with CeO2 primary crystal grains on the surface. 4g of Ce(NO3)3·6H2O, 7g of PVP, and 98ml of ethylene glycol solution were mixed and placed at 75°C. o Stir at temperature C for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of ethylene glycol solution containing Fe3O4@CeO2 nanoparticles with primary CeO2 crystals, and heat to 155 °C. o C, react for 2 hours, wash with pure water and ethanol to obtain Fe3O4@CeO2 magnetic core-shell nanoparticles with a uniform CeO2 shell on the surface.

[0130] Figure 15 (a) is a SEM image of Fe3O4 nanoparticles; (b) is a SEM image of Fe3O4@CeO2 core-shell nanoparticles prepared in this embodiment. It can be seen that Fe3O4@CeO2 core-shell nanoparticles have good monodispersity, uniform shell, no roughness or agglomeration on the particle surface, and the average particle size of Fe3O4@CeO2 core-shell nanoparticles is 146 nm.

[0131] Example 10

[0132] A type of nanocore-shell particle comprising Fe3O4 particles, epigallocatechin gallate (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0133] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 9. The polyhydroxy compound used to modify the surface of the Fe3O4 core particles is epigallocatechin gallate. The prepared Fe3O4@CeO2 core-shell nanoparticles have good monodispersity, uniform shell, and no roughness or agglomeration on the particle surface. The average particle size of the Fe3O4@CeO2 core-shell nanoparticles is 148 nm.

[0134] Example 11

[0135] A type of nanocore-shell particle comprising Fe3O4 particles, kaempferol (a polyhydroxy compound), and cerium oxide (a metallic compound shell).

[0136] The preparation method of the above-mentioned core-shell nanoparticles is the same as that in Example 9, except that the polyhydroxy compound modified on the surface of the Fe3O4 core particles is kaempferol. The prepared Fe3O4@CeO2 core-shell nanoparticles have good monodispersity, uniform shell, and no roughness or agglomeration on the particle surface. The average particle size of the Fe3O4@CeO2 core-shell nanoparticles is 140 nm.

[0137] Example 12

[0138] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and zinc sulfide (a metallic compound shell).

[0139] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0140] S1. Preparation of Fe3O4@tannic acid nanoparticles: 130nm Fe3O4 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and then centrifuged to obtain tannic acid-modified Fe3O4 particles (Fe3O4@tannic acid).

[0141] Synthesis of S2..Fe3O4@ZnS core-shell nanoparticles: 2g Zn(NO3)2·6H2O, 1g TU, 1g PVP, and 98ml ethylene glycol solution were mixed and placed at 60°C. o Stir at temperature C for 30 minutes until the reactants are completely dispersed in the solvent. Add 2 ml of ethylene glycol solution of Fe3O4@tannic acid and heat to 125°C. o At C, the reaction was carried out for 3 hours, followed by washing with pure water and ethanol to obtain Fe3O4@ZnS nanoparticles with ZnS primary crystal grains on the surface. 2g Zn(NO3)2·6H2O, 1g TU, 1g PVP, and 98ml ethylene glycol solution were mixed and placed at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of ethylene glycol solution containing Fe3O4@ZnS nanoparticles with primary ZnS crystals, and heat to 125 °C. o C, react for 30 min, wash with pure water and ethanol to obtain Fe3O4@ZnS nanocore-shell particles with a ZnS shell on the surface.

[0142] The method for preparing the above-mentioned core-shell nanoparticles into a magnetically responsive photonic crystal is as follows: Take 5 mg of the above-prepared Fe3O4@ZnS core-shell nanoparticles and disperse them in 0.5 ml of ethanol containing 0.5 mg PVP. After ultrasonic dispersion, the magnetically responsive photonic crystal is obtained.

[0143] Figure 16 (a) is a SEM image of Fe3O4 nanoparticles; (b) is a SEM image of Fe3O4@ZnS core-shell nanoparticles prepared in this embodiment. The core-shell nanoparticles are spherical and uniform, with good monodispersity and no agglomeration.

[0144] Example 13

[0145] A type of core-shell nanoparticle comprising Fe3O4 particles, tannic acid (a polyhydroxy compound), and zinc oxide (a metallic compound shell).

[0146] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0147] S1. Preparation of Fe3O4@tannic acid nanoparticles: 130nm Fe3O4 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and then centrifuged to obtain tannic acid-modified Fe3O4 particles (Fe3O4@tannic acid).

[0148] Synthesis of S2.Fe3O4@ZnO core-shell nanoparticles: 1g Zn(Zc)2·2H2O, 2g PVP, and 98ml N,N-dimethylformamide solution were mixed and placed at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent, then add 2 ml of Fe3O4@tannic acid aqueous solution and heat to 100°C. o C, react for 1 h, wash with pure water and ethanol to obtain Fe3O4@ZnS nanoparticles with ZnO primary crystal grains on the surface. Mix 1 g Zn(Zc)2·2H2O, 2 g PVP, and 98 ml N,N-dimethylformamide solution, and place at 60 °C. o Stir at C for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of N,N-dimethylformamide solution containing Fe3O4@ZnO nanoparticles with primary ZnO crystals, and heat to 100°C. o C, react for 1 hour, wash with pure water and ethanol to obtain Fe3O4@ZnO nanocore-shell particles with a ZnO shell on the surface.

[0149] Example 14

[0150] A type of core-shell nanoparticle comprising CeO2 particles, tannic acid (a polyhydroxy compound), and ZnS (a metal compound shell).

[0151] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0152] S1. Preparation of CeO2@tannic acid nanoparticles: 120nm CeO2 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and centrifuged to obtain tannic acid modified CeO2 particles (CeO2@tannic acid).

[0153] Synthesis of S2.CeO2@ZnS core-shell nanoparticles: 2g Ce(NO3)3·6H2O, 1g TU, 1g PVP, and 98ml ethylene glycol solution were mixed and placed at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent, then add 2 ml of CeO2@tannic acid ethylene glycol solution, and heat to 125°C. o C, react for 1 h, wash with pure water and ethanol to obtain CeO2@ZnS nanoparticles with ZnS primary crystal grains on the surface. Mix 2g Ce(NO3)3·6H2O, 1g TU, 1g PVP, and 98ml ethylene glycol solution, and place at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of ethylene glycol solution containing CeO2@ZnS nanoparticles with primary ZnS crystals, and heat to 125 °C. o C, react for 2 hours, wash with pure water and ethanol to obtain CeO2@ZnS nanocore-shell particles with a ZnS shell on the surface.

[0154] Example 15

[0155] A type of core-shell nanoparticle comprising CeO2 particles, tannic acid (a polyhydroxy compound), and CdS (a metal compound shell).

[0156] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0157] S1. Preparation of CeO2@tannic acid nanoparticles: 120nm CeO2 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and centrifuged to obtain tannic acid modified CeO2 particles (CeO2@tannic acid).

[0158] Synthesis of S2.CeO2@CdS core-shell nanoparticles: 2g Cd(NO3)2·4H2O, 1g TU, 1.5g PVP, and 98ml polyethylene glycol solution were mixed and placed at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent, then add 2 ml of a polyethylene glycol solution containing CeO2@tannic acid, and heat to 130°C. oAt C, the reaction was carried out for 1 hour, followed by washing with pure water and ethanol to obtain CeO2@CdS nanoparticles with CdS primary crystal grains on the surface. 2g Cd(NO3)2·4H2O, 1g TU, 1.5g PVP, and 98ml polyethylene glycol solution were mixed and placed at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of polyethylene glycol solution containing CeO2@CdS nanocore-shell particles with primary CdS crystals, and heat to 130°C. o C, react for 2 hours, wash with pure water and ethanol to obtain CeO2@CdS nanocore-shell particles with a CdS shell on the surface.

[0159] Example 16

[0160] A type of core-shell nanoparticle comprising CeO2 particles, tannic acid (a polyhydroxy compound), and Fe3O4 (a metallic compound shell).

[0161] The preparation method of the above-mentioned core-shell nanoparticles includes the following steps:

[0162] S1. Preparation of CeO2@tannic acid nanoparticles: 120nm CeO2 particles and tannic acid with a mass ratio of 20:1 were added to 5ml of ethanol, ultrasonically complexed for 5min at room temperature, and centrifuged to obtain tannic acid modified CeO2 particles (CeO2@tannic acid).

[0163] Synthesis of S2.CeO2@Fe3O4 core-shell nanoparticles: 2g Fe(Cl)3·6H2O, 10g PVP, 8g NaAc, and 98ml ethylene glycol solution were mixed and placed at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent, then add 2 ml of CeO2@tannic acid ethylene glycol solution, and heat to 220°C. o C, react for 1 h, wash with pure water and ethanol to obtain CeO2@Fe3O4 nanoparticles with Fe3O4 primary crystal grains on the surface. Mix 2g Fe(Cl)3·6H2O, 10g PVP, 8g NaAc, and 98ml ethylene glycol solution, and place at 60°C. o Stir at C temperature for 30 min until the reactants are completely dispersed in the solvent. Add 2 ml of ethylene glycol solution containing CeO2@Fe3O4 nanocore-shell particles with primary Fe3O4 crystals, and heat to 220°C. o C, react for 1 hour, wash with pure water and ethanol to obtain CeO2@Fe3O4 nanocore-shell particles with Fe3O4 shell on the surface.

[0164] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0165] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A core-shell nanoparticle, characterized in that: The nanoparticles include a core containing a metal element, a shell containing a metal element, and a polyhydroxy compound connecting the core and shell. The polyhydroxy compound is a polyphenolic compound, including flavonoids, flavonols, catechins, phenolic acids, lignans, tannins, and anthocyanins, specifically at least one of apigenin, kaempferol, epicatechin, epigallocatechin, epigallocatechin gallate, gallic acid, enterodiol, tannic acid, proanthocyanidins, cyanidin-3-O-glucoside, and pyrogallol. When these core-shell nanoparticles are applied in the field of photonic crystals, the brightness of the structural color can be enhanced when assembling structural colors under the influence of an electric field and / or magnetic field. The nanoparticle core is a black monodisperse magnetic nanoparticle; the shell is a light chemical color and includes at least one element, alloy, oxide, or sulfide of zinc, cerium, cadmium, aluminum, vanadium, chromium, tin, europium, gadolinium, zirconium, tungsten, titanium, and indium; the nanoparticle core and shell have different material compositions. The average thickness of the shell is 5-400 nm.

2. The nanocore-shell particles according to claim 1, characterized in that: The nanoparticle core is an element, alloy, oxide, or sulfide of at least one of iron, cobalt, and nickel.

3. The nanocore-shell particles according to claim 1, characterized in that: The nanoparticle core is iron(III) oxide.

4. The nanocore-shell particles according to claim 1, characterized in that: The shell is at least one of CeO2, ZnO, ZnS, and CdS.

5. The core-shell nanoparticles according to claim 1, characterized in that: The average particle size of the nanoparticle core is 5-500 nm.

6. A method for preparing nano-core-shell particles according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of nanoparticle cores containing metal elements with surface-coordinated complexation modified polyhydroxy compounds; (2) Prepare a precursor solution for synthesizing a shell containing metal elements, mix the prepared nanoparticle core with the precursor solution, and coat the nanoparticle core with the shell at the reaction temperature to obtain the nano core-shell particles.

7. The method for preparing nano-core-shell particles according to claim 6, characterized in that: In step (1), when the nanoparticle core complexes with the polyhydroxy compound, the concentration of the polyhydroxy compound in the solution is between 0.1 mg / ml and saturation concentration.

8. The method for preparing nano-core-shell particles according to claim 6, characterized in that: In step (2), the precursor liquid includes a metal source, an additive and a solvent; or a metal source, a sulfur source, an additive and a solvent.

9. The method for preparing nano-core-shell particles according to claim 8, characterized in that: The metal source is a soluble salt of a metal, the sulfur source is at least one of sodium sulfide, ammonium sulfide, thioacetamide, and thiourea, the additive includes a dispersant, the dispersant is at least one of anionic surfactant, cationic surfactant, and nonionic surfactant, and the solvent is a solution capable of dissolving the above-mentioned metal source or the metal source, sulfur source, and dispersant.

10. The application of a core-shell nanoparticle according to any one of claims 1-5 or a core-shell nanoparticle prepared by the preparation method according to any one of claims 6-9, characterized in that: The nano-core-shell particles are applied to the field of photonic crystal optics.

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