KR101168653B1 - Process for Preparing Nanodendrites - Google Patents

Abstract

The present invention relates to a method capable of easily mass-producing platinum nano dendrites in which platinum nanocrystals are formed in a dendritic structure on gold nanocrystals in high yield. Platinum nano dendrites prepared according to the production method of the present invention is remarkably excellent in the electrocatalyst activity against the oxygen reduction reaction (ORR).

Description

Process for Preparing Nanodendrites

The present invention relates to a method for producing nano dendrites. More specifically, the present invention relates to a method capable of easily mass-producing platinum nano dendrites in which platinum nanocrystals are formed in a dendritic structure on gold nanocrystals in high yield.

Platinum and its alloys have been used in various industries such as CO / NO _x oxidation, nitric acid synthesis, oil cracking and fuel cells in catalytic converters. In particular, platinum has been used as the most effective catalyst in proton-exchange membrane fuel cells (PEMFCs) because of its excellent electrocatalyst properties that promote both hydrogen oxidation and oxygen reduction. Although carbon-supported platinum nanoparticles are currently used as cathode catalysts in fuel cell technology, they are more economical and effective catalysts that can operate while using much less expensive platinum in commercial applications. Development of the material is needed.

Recently, efforts have been made to improve the electrocatalyst performance of platinum-based materials by controlling the shape of platinum nanocrystals or by alloying platinum with other transition metals. In particular, platinum nanodendrite having a dendritic structure composed of many edge and corner atoms recently developed exhibits significantly increased catalytic activity for oxygen reduction reaction (ORR). Although known, no method has been reported for mass production of platinum nanodendrite.

According to the conventional manufacturing method, only a few mg of platinum nanodendrite is prepared per 1 ml of reaction suspension, and a platinum nanodendrite having a surface-coated surfactant is prepared to remove the surfactant that lowers the catalytic activity. However, since the process of removing the surfactant is generally a harsh condition, there was a problem that often occurs deformation of the nanocrystals and reduction of catalytic activity.

The present inventors have found that the growth of platinum nanodendrite can be easily mass-produced without a surfactant by growth with gold seeds in a cavity of porous silica nanospheres and completed the present invention.

Accordingly, an object of the present invention is to provide a method for mass production of platinum nano dendrites easily in high yield.

The present invention relates to a method for producing platinum nano dendrites in which platinum nanocrystals are formed in a dendritic structure on gold nanocrystals.

(i) Platinum salts are reacted with a reducing agent in an aqueous suspension comprising a hollow porous silica nanoshell and a nanorattle structure comprising the entrapped gold nanocrystals to react the porous silica with a reducing agent. Obtaining a platinum nanodendrite coated with a shell; And

(ii) removing the porous silica shell from the platinum nanodendrite coated with the porous silica shell.

In the step (i), when the metal salt is reacted with a reducing agent in the aqueous suspension including the nanorattle structure, the nanorattle structure acts as a nano-reactor so that the platinum nanocrystals in the dendritic structure of the gold nanocrystal seeds Platinum nano dendrites coated with porous silica shells formed by growth are produced.

In the nanorattle structure, the size of the gold nanocrystals is preferably 2 to 10 nm, the size of the cavity is preferably 10 to 50 nm, and the size of the nano rattle structure is preferably 20 to 100 nm.

The platinum salt may be used as nitrate, sulfate, oxalate, phosphate, chloride, bromide, acetate, etc. of platinum, but is not limited thereto. Preferably Na ₂ PtCl ₄ , K ₂ PtCl ₄ , Na ₂ PtCl ₆ , K ₂ PtCl ₆ , PtCl ₂ or Pt (NO ₃ ) ₂ is used.

The reducing agent may be hydrazine, hydrogen peroxide, ascorbic acid, hydroxylamine, citric acid, alcohol, phosphorus, NaBH ₄ and the like, but is not limited thereto. Preferably ascorbic acid, hydrazine or NaBH ₄ are used.

In step (i), the platinum nanodendrite grows only in the shell of the cavity to produce nanoparticles in which the platinum nanodendrite is well coated with the porous silica shell.

Increasing the initial concentration of platinum salts results in the formation of larger platinum nanocrystals, and the size of the nanocrystals does not increase beyond a certain size even if the concentration of the platinum salts increases further. This means that platinum preferentially nucleates the gold surface in the cavity and then gradually grows, and growth is limited by the cavity size.

When using nanorattle structures free of gold nanocrystals, or nanorattle structures containing gold nanoparticles stabilized with citrate, large platinum particles grow on the outer surface of the silica shell, or large amounts of platinum nanoparticles, respectively. Aggregates are formed.

Removal of the porous silica shell in the step (ii) is preferably carried out by treating the platinum nano dendrites coated with the porous silica shell with a base solution. Specifically, the porous silica shell may be dissolved by dissolving the platinum nanodendrite coated with the porous silica shell in the base solution, or by adding the base solution to the suspension of the platinum nanodendrite coated with the porous silica shell and stirring. At this time, the platinum nano dendrites are easily separated without deformation of the form.

Sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like may be used as the base, but is not limited thereto.

According to the preparation method of the present invention, the platinum nanodendrite coated with the porous silica shell obtained in step (i) is isolated and purified and then used in step (ii) or without steps (i) and (ii) ) Can be carried out continuously in the same reactor.

FIG. 2 is a view schematically illustrating a manufacturing process of platinum nano dendrites having platinum nanocrystals formed in a dendritic structure in gold nanocrystals according to an embodiment of the present invention.

On the other hand, the nanorattle structure including the porous silica nanoshell of the cavity and gold nanocrystals trapped in the cavity

(a) Hybrid nanocrystals and silica nanoshells in which the gold nanocrystals are attached to the iron oxide nanocrystals by encapsulation of the iron oxide nanocrystals with the gold ion complex in the presence of a polyethylene glycol-based surfactant. Obtaining a silica nanosphere comprising a; And

(b) treating the silica nanospheres with sodium borohydride to reductively decompose the iron oxide nanocrystals and etch the silica nanoshells.

The encapsulation reaction of step (a) can be carried out using a known reverse microemulsion method (DK Yi, SS Lee, GC Papaefthymiou and JY Ying, Chem. Mater . 2006, 18 , 614; DC Lee, FV Mikulec, JM Pelaez, B. Koo and BA Korgel, J. Phys. Chem. B , 2006, 110 , 11160]. Specifically, an aqueous solution containing the iron oxide nanocrystals stabilized with oleic acid and a gold ion complex was mixed in a cyclohexane solution containing a surfactant to include a water droplet containing the gold ion complex and an external cyclohexane phase containing the iron oxide nanocrystals. After forming an inverted microemulsion system, an aqueous ammonium hydroxide solution and tetraethylorthosilicate (TEOS) may be added successively to form a silica shell around the iron oxide nanocrystals.

Most preferably, Fe ₃ O ₄ is used as the iron oxide in step (a), Au ³⁺ complex is preferably used as the gold ion complex, and HAuCl ₄ is most preferably used. Moreover, it is most preferable to use polyoxyethylene nonyl phenyl ether as polyethylene glycol type surfactant.

The formation of the hybrid nanocrystal in the step (a) is considered to be because gold ions are reduced by the polyethylene glycol-based surfactant, and gold preferentially nucleates on the iron oxide surface.

In step (b), when the nanospheres are treated with sodium borohydride, only iron oxide crystals are rapidly removed from the iron oxide / gold hybrid nanocrystals through a reduction decomposition process. This is facilitated by the deposited gold crystals, and the iron oxide crystals do not decompose in the absence of the attached gold crystals.

By selectively decomposing iron oxide with sodium borohydride in step (b) and etching the silica, gold nanocrystals remain in the cavity of the porous porous silica nanoshells, resulting in the nanorattle structure.

The cavity size of the resulting nanorattle structures is generally larger than the iron oxide particles removed, which is believed to be due to the etching of the resulting cavity surface after iron oxide decomposition.

Gold nanocrystals are also believed to be due to the coalescence or ripening of gold particles in the cavity during the etching reaction.

According to the above production method, the cavity size of the resulting nanorattle structure can be easily adjusted by changing the size of the iron oxide nanocrystals used.

FIG. 2 is a view schematically illustrating a process of manufacturing a nanorattle structure using Fe ₃ O ₄ as iron oxide and HAuCl ₄ as a gold ion complex.

According to the production method of the present invention, it is possible to easily mass-produce platinum nano dendrites in which platinum nanocrystals are formed in a dendritic structure on gold nanocrystals in high yield. In one embodiment, according to the method of the present invention, 1.5 g of uniform platinum nanodendrite can be synthesized in 40 ml of an aqueous suspension.

In addition, according to the production method of the present invention, it is possible to prepare the platinum nano dendrites of the desired form even from a high concentration of the reaction suspension, and unlike the prior art, since it is produced without a surfactant, it is necessary to perform a further surfactant removal process. There is no. In addition, since there is no surfactant, it is possible to simply attach functional ligand molecules to impart various properties and functions to the surface.

Platinum nano dendrites prepared according to the production method of the present invention is remarkably excellent in the electrocatalyst activity against the oxygen reduction reaction (ORR).

1 is a view schematically showing a manufacturing process of platinum nano dendrites according to an embodiment of the present invention.
FIG. 2 is a view schematically illustrating a process of manufacturing a nanorattle structure using Fe ₃ O ₄ as iron oxide and HAuCl ₄ as a gold ion complex.
3 is a transmission electron microscope image of silica nanospheres (Fe ₃ O ₄ / Au @ SiO ₂ ) including Fe ₃ O ₄ / Au hybrid nanocrystals prepared in Preparation Example 1 and silica nanospheres, Fe ₃ O ₄ particles And a histogram showing the size distribution of Au particles.
4 is a histogram showing the transmission electron microscope image of the nano rattle structure (Au @ h-SiO ₂ ) including the gold nanocrystals prepared in Preparation Example 2 and the size distribution of silica nanospheres, cavities, and Au particles.
FIG. 5 (a) is a diagram showing an X-ray diffraction pattern of silica nanospheres (Fe ₃ O ₄ / Au @ SiO ₂ ) containing Fe ₃ O ₄ / Au hybrid nanocrystals prepared in Preparation Example 1, FIG. 5 (b) is a diagram showing an X-ray diffraction pattern of a nano rattle (Au @ h-SiO ₂ ) containing gold nanocrystals prepared in Preparation Example 2. FIG.
6 is a histogram (bottom middle) showing the size distribution of the platinum nanodendrite and the transmission electron microscope image (right) of the platinum nano dendrites (Pt @ SiO ₂ ) coated with the porous silica shell prepared in Example 1. FIG. .
FIG. 7 is a scanning electron microscope image of platinum nano dendrites (Pt @ SiO ₂ ) coated with a porous silica shell prepared in Example 1. FIG.
FIG. 8 is a diagram showing an X-ray diffraction pattern of platinum nano dendrites (Pt @ SiO ₂ ) coated with a porous silica shell prepared in Example 1. FIG.
FIG. 9 is a diagram showing a high resolution transmission electron microscope image and a selected region electron diffraction pattern (insertion diagram) of platinum nano dendrites (Pt @ SiO ₂ ) coated with a porous silica shell prepared in Example 1. FIG.
10 is a transmission electron microscope image of the platinum nano dendrites (Lf-PtND) prepared in Example 2.
FIG. 11 is a transmission electron microscope image of platinum nano dendrites (Pt @ SiO ₂ ) and platinum nano dendrites (Lf-PtND) (inset) coated with a porous silica shell prepared in Example 4. FIG.
12 is an oxygen reduction reaction polarization curve and mass activity and inactivity for platinum nano dendrites (Lf-PtND) prepared in Example 2, commercially available platinum black catalysts and spherical Pt / Au alloy nanocrystals prepared in Comparative Example 1. FIG. (Inset diagram)

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are for illustrative purpose only and that the scope of the present invention is not limited to these embodiments.

Preparation Example 1 Fe ₃ O ₄ / Nu Silica Nanospheres Containing Hybrid Nanocrystals (Fe ₃ O ₄ / Au @ SiO ₂ )

Fe ₃ O ₄ nanocrystals having an average core size of 8 nm were obtained according to known methods [Ref. Park, J .; An, K .; Hwang, Y .; Park, J.-G .; Noh, H.-J .; Kim, J.-Y .; Park, J.-H .; Hwang, N.-M .; Hyeon, T. Nat. Mater . 2004, 3 , 891].

Polyoxyethylene (5) nonylphenyl ether (7.68 g, 18.0 mmol, Igepal CO-520, containing 50 mol% hydrophilic group, Aldrich) was dispersed by stirring in a round bottom flask containing cyclohexane (170 ml). Then, 8.0 mg of Fe ₃ O ₄ nanocrystals obtained above dispersed in cyclohexane were added to the reaction solution. The resulting mixture was vortexed until clear. HAuCl ₄ aqueous solution (24 mM, 0.5 ml) and ammonium hydroxide solution (30%, 1.3 ml) were added successively to the reaction mixture to form a clear suspension. Then, tetraethylorthosilicate (TEOS; 1.5 ml) was added and stirred for 12 hours. Silica nanospheres (Fe ₃ O ₄ / Au @ SiO ₂ ) containing the resulting Fe ₃ O ₄ / Au hybrid nanocrystals were collected by magnetic decantation. The collected nanospheres (Fe ₃ O ₄ / Au @ SiO ₂ ) were redispersed in ethanol and recovered using a magnet. The process of dispersing Fe ₃ O ₄ / Au @ SiO ₂ in an ethanol suspension and separating magnetically was purified three times.

The resulting solids were analyzed by X-ray photoelectron spectrometry (XPS), and it was confirmed that Au (3+) was reduced to form Au (0) during the reaction.

In addition, the results of analyzing the generated solids with a transmission electron microscopy (TEM) are shown in FIG. In Figure _3, Fe 3 O ₄ nano the crystal growth is small Au nanocrystals of around 1 to 2 nm diameter several, Fe ₃ O ₄ / Au hybrid nanocrystals 29 (± 1) nm silica nanoparticles with a diameter including the old It can be seen that (Fe ₃ O ₄ / Au @ SiO ₂ ) is produced.

Preparation Example 2 Nano Rattle Structure Containing Gold Nanocrystals (Au @ h-SiO ₂ Manufacturing

An aqueous NaBH ₄ solution (0.2 M, 1.0 ml) was added to an aqueous 2.0 ml suspension containing 1.0 mg of Fe ₃ O ₄ / Au @ SiO ₂ obtained in Preparation Example 1 and stirred at room temperature for 30 minutes. The dark brown color of the suspension gradually faded away as hydrogen gas was released. The nanorattle structure (Au @ h-SiO ₂ ) comprising the resulting gold nanocrystals and the cavity's porous silica shell was collected by centrifugation. The process of dispersing Au @ h-SiO ₂ in an aqueous suspension and centrifuging was purified three times.

The results of analysis by TEM and X-ray diffraction (XRD) of the resulting solids are shown in FIGS. 4 and 5, respectively. 4 and 5, Fe ₃ O ₄ is decomposed and removed from the hybrid nanocrystals to form a cavity of 14 (± 2) nm diameter in the silica nanospheres, thereby forming a porous porous silica having an outer diameter of 28 (± 2) nm. It can be seen that a rattle-type nanostructure (Au @ h -SiO ₂ ) composed of the shell and Au nanocrystals having an average size of 4 (± 1) nm is formed.

Example 1: Platinum Nano Dendrites Coated with Porous Silica Shell (Pt @ SiO) ₂ Manufacturing

0.5 mg of Au @ h- SiO ₂ nanospheres obtained in Preparation Example 2 and 3.5 mg of L-ascorbic acid were mixed in 0.22 ml of distilled water. To the mixed suspension was added dropwise 1.0 ml of an aqueous solution containing 2.0 mg of Na ₂ PtCl ₄ . The initial concentration of Na ₂ PtCl ₄ in the reaction suspension was 1.6 mg / ml. The reaction was carried out for 2 hours with gentle stirring at room temperature, and then the resulting platinum silica dendrites (Pt @ SiO ₂ ) coated with the porous silica shell were collected by centrifugation, then redispersed in an aqueous suspension and centrifuged. The process was repeated three times to obtain a black powder.

The results of TEM and scanning electron microscopy (SEM) analysis of the obtained black powder (Pt @ SiO ₂ ) are shown in FIGS. 6 and 7, respectively. From Figures 6 and 7, it was confirmed that the platinum species grows only within the cavity to produce Pt @ SiO ₂ nanospheres in which three-dimensional flower-shaped Pt-on-Au nanocrystals are well coated with porous silica shells. It was. In addition, a histogram showing the size distribution of platinum nano dendrites in the obtained black powder (Pt @ SiO ₂ ) is shown in FIG. 6.

Meanwhile, XRD analysis of the obtained black powder (Pt @ SiO ₂ ) is shown in FIG. 8. The XRD pattern showed the formation of platinum crystals with face centered cubic crystal phase.

In addition, the results of high resolution (HR) TEM and selective area electron diffraction (SAED) analysis of the obtained black powder (Pt @ SiO ₂ ) are shown in FIG. 9. From FIG. 9, it was confirmed that the grown nanocrystals had a three-dimensional dendritic structure in which platinum arms were interconnected. Each platinum arm had an average size of 3.0 (± 0.4) nm and exhibited a single crystal structure mainly by (111) facet and a small portion of (311) face, which was selected region electron diffraction obtained during TEM analysis (selective area electron diffraction: SAED) pattern.

In addition, according to inductively coupled plasma-atomic emission spectroscopy (ICP-AES), the weight percentage of platinum in the 15 (± 2) nm platinum nanodendrite was 99%.

Example 2: Preparation of Platinum Nanodendrite (Lf-PtND)

1.2 mg of the purified solid (Pt @ SiO ₂ ) obtained in Example 1 was dispersed in 10 ml of 2.0 M NaOH suspension and stirred at room temperature to dissolve the silica shell of Pt @ SiO ₂ . The solids produced from the reaction suspension were separated by centrifugation and purified by repeating the process of redispersing a solid surface (Ligand-free Pt Nanodendrite (Lf-PtND) without surfactants) into an aqueous suspension and centrifuging.

The result of TEM analysis of the obtained solid (Lf-PtND) is shown in FIG. 10. It was confirmed that the form of the platinum nano dendrites is maintained in the process of removing the silica shell from FIG.

Example 3: One Step Preparation of Platinum Nanodendrite (Lf-PtND)

55.6 mg Au @ h- SiO ₂ nanospheres obtained in Preparation Example 2 (39.7 mg / ml), 146.0 mg L-ascorbic acid (104.6 mg / ml) and 200.0 mg Na ₂ PtCl ₄ (142.8 mg / ml ) Was reacted for 3 hours. 10 ml of 2.0 M NaOH solution was slowly added to 1.2 ml of the reaction suspension while cooling with an ice bath and stirred at room temperature for 1 hour. The Lf-PtND generated from the reaction suspension was separated by centrifugation, re-suspended in water and centrifuged to purify it repeatedly.

Example 4 Mass Production of Platinum Nanodendrite (Lf-PtND)

1.8 g of Au @ h- SiO ₂ nanospheres and 2.6 g of L-ascorbic acid obtained in the same manner as in Preparation Examples 1 and 2 were mixed in 21 ml of an aqueous suspension. Then, 19 ml of 0.5 M Na ₂ PtCl ₄ solution was added dropwise to the mixed suspension for 1 minute and stirred at room temperature for 3 hours. The resulting solid (Pt @ SiO ₂ ) was collected by centrifugation, and the process of dispersion and centrifugation with an aqueous suspension was purified three times. The purified solid (Pt @ SiO ₂ ) was redispersed in 300 ml of 2.0 M NaOH solution and stirred at room temperature for 3 hours. The resulting solid (Lf-PtND) was collected by centrifugation and purified by washing with water. The resulting solid was dried under vacuum to afford 1.5 g of the title compound as a black powder (total yield: 81%, based on the amount of Pt).

TEM analysis results of the prepared Pt @ SiO ₂ and Lf-PtND are shown in FIG. 11.

The nitrogen adsorption-desorption isotherm of the Lf-PtND powder exhibited a large surface area of 25 m ² / g, which can be expected to enhance the catalytic performance.

Comparative Example 1: Preparation of spherical Pt / Au alloy nanocrystals

20.0 mg of Pt @ SiO ₂ powder obtained in Example 1 was heated in a furnace at a heating rate of 5 ° C./min and annealed at 400 ° C. for 2 hours under a flow of Ar + 4% H ₂ . The annealed powder containing spherical Pt / Au nanocrystals in the cavity was dispersed in 10 ml of 2.0 M NaOH solution and stirred at room temperature for 1 hour. The nanocrystals produced from the suspension were separated by centrifugation, and the processes of redispersion and centrifugation were repeated and purified.

Test Example 1 Measurement of Electrocatalytic Activity

To evaluate the effect of platinum nanodendrite (Lf-PtND) as a cathode catalyst in proton-exchange membrane fuel cells (PEMFC), Lf-PtND on oxygen reduction reaction (ORR) Was compared with commercially available platinum black catalysts (Alfa Aesar, HiSPEC ^™ fuel cell grade) and spherical Pt / Au alloy nanocrystals prepared in Comparative Example 1.

ORR polarization obtained in O ₂ -saturated 0.1 M HClO ₄ electrolyte solution using glassy carbon rotating disk electrode (RDE; 1600 rpm) filled with 15.3 μg / cm ² of catalyst The curve (scan speed: 10 mV / s) is shown in FIG.

12, it can be seen that the polarization curve of Lf-PtND shows a positive directional shift of about 140 mV at both half wavelength and starting potential as compared to the spherical Pt / Au alloy nanocrystals. Therefore, it was confirmed that the electrocatalyst performance of Lf-PtND was significantly improved compared to the spherical nanocrystals. The mass activity and specific activity of Lf-PtND against ORR at 0.85 V was much greater than that of the spherical Pt / Au alloy nanocrystals, which showed that the effect of the dendritic platinum nanocrystals as ORR catalysts was spherical. Prove better. Significantly increased electrocatalytic activity of Lf-PtND is due to the presence of a large number of edge and corner atoms as well as a large catalytically effective surface area. The electrocatalyst surface area (ECSA) of Lf-PtND was 3.5 times larger than the spherical Pt / Au alloy nanocrystals when compared based on the mass of the platinum catalyst. In addition, Lf-PtND exhibited about four times more mass activity than commercially available platinum black catalysts, indicating that it is economically promising to use Lf-PtND as an ORR catalyst.

Claims (11)

As a manufacturing method of platinum nano dendrites in which platinum nanocrystals are formed in a dendritic structure on gold nanocrystals,
(i) Platinum salts are reacted with a reducing agent in an aqueous suspension comprising a hollow porous silica nanoshell and a nanorattle structure comprising the entrapped gold nanocrystals to react the porous silica with a reducing agent. Obtaining a platinum nanodendrite coated with a shell; And
(ii) removing the porous silica shell from the platinum nano dendrites coated with the porous silica shell. The method of claim 1, wherein the size of the gold nanocrystals is 2 to 10 nm, the size of the cavity is 10 to 50 nm, and the size of the nanorattle structure is 20 to 100 nm. The method according to claim 1, characterized in that in step (i) Na ₂ PtCl ₄ , K ₂ PtCl ₄ , Na ₂ PtCl ₆ , K ₂ PtCl ₆ , PtCl ₂ or Pt (NO ₃ ) ₂ is used as the platinum salt. Manufacturing method. The process according to claim 1, wherein ascorbic acid, hydrazine or NaBH ₄ is used as reducing agent in step (i). The method according to claim 1, wherein the removal of the porous silica shell in step (ii) is carried out by treating the platinum nanodendrite coated with the porous silica shell with a base solution. 6. The process according to claim 5, wherein sodium hydroxide, potassium hydroxide or ammonium hydroxide is used as the base. The process according to claim 1, wherein steps (i) and (ii) are carried out continuously in the same reactor. The nanorattle structure of claim 1, wherein the nanorattle structure comprises a porous silica nanoshell of the cavity and gold nanocrystals trapped in the cavity.
(a) Hybrid nanocrystals and silica nanoshells in which the gold nanocrystals are attached to the iron oxide nanocrystals by encapsulation of the iron oxide nanocrystals with the gold ion complex in the presence of a polyethylene glycol-based surfactant. Obtaining a silica nanosphere comprising a; And
(b) treating the silica nanospheres with sodium borohydride to reductively decompose the iron oxide nanocrystals and etch the silica nanoshells. The process according to claim 8, wherein in step (a) Fe ₃ O ₄ is used as the iron oxide and HAuCl ₄ is used as the gold ion complex. The gold ion complex according to claim 8, wherein the encapsulation reaction of step (a) is mixed with an aqueous solution containing iron oxide nanocrystals stabilized with oleic acid and a gold ion complex in a cyclohexane solution containing a polyethylene glycol-based surfactant. Forming a reverse microemulsion system comprising a water droplet containing water and an external cyclohexane phase containing iron oxide nanocrystals, and then successively adding aqueous ammonium hydroxide solution and tetraethylorthosilicate (TEOS). Manufacturing method. The method according to claim 10, wherein Fe ₃ O ₄ is used as the iron oxide, HAuCl ₄ is used as the gold ion complex, and polyoxyethylene nonylphenyl ether is used as the polyethylene glycol-based surfactant.

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