TWI454315B - Hollow metal sphere with mesoporous structure and method for manufacturing the same - Google Patents

Description

Metal hollow sphere with mesoporous structure and manufacturing method thereof

The invention relates to a metal hollow sphere with a mesoporous structure and a manufacturing method thereof, in particular to a metal hollow sphere having a shell composed of mesopores arranged symmetrically in Ia3d and a manufacturing method thereof.

Metal nanostructures play a key role in energy-related photoelectrocatalytic reactions, green chemical-related catalytic reactions, and nanomedical tests, such as platinum-based anode-anode electrocatalysts for fuel cells, and are used in various applications. A nano-gold catalyst which oxidizes and catalyzes other reactions, and a palladium catalyst which is used in many organic catalytic reactions.

More specifically, as environmental awareness gradually rises, hydrogen fuel cell systems that reduce environmental pollution and reduce carbon dioxide emissions are gaining market attention. Among them, the fuel cell is widely used, and can be applied to a large generator, a rocket energy supply, a motor vehicle energy supply, and the like. In addition, as fuel cells are gradually becoming more and more miniaturized, fuel cells can be applied to portable electronic products such as mobile phones, laptop computers, and digital cameras.

In general, when a metal nanocatalyst is used, since it is unstable in structure and tends to form large particles, it is required to be supported on a suitable high surface area carrier to carry out the reaction. However, when a carrier is used, problems such as the carrier participating in the reaction or indirectly affecting the chemical properties of the metal catalyst may occur. Therefore, many studies are currently devoted to the development of metal nanostructures with stable structures in order to develop metal nanostructures that can undergo catalytic reactions without the need for carriers.

Therefore, it is urgent to develop a metal hollow sphere with a mesoporous structure and a manufacturing method thereof, so that a metal hollow sphere having a regular mesoporous structure can be produced in a simple manner to increase the reaction surface area of the metal hollow sphere. Improve the reaction efficiency of the metal nanocatalyst.

The main object of the present invention is to provide a method for manufacturing a metal hollow sphere having a mesoporous structure, which can be manufactured by a simple process with a nanometer size, a uniform particle size, a thickness of the shell layer, and a mesoporous pore size. Tune the metal hollow ball.

Another object of the present invention is to provide a metal hollow sphere having a mesoporous structure having a through-shell passage and having a regular mesoporous arrangement to enhance the catalytic efficiency of the metal hollow sphere.

To achieve the above object, the method for fabricating a metal hollow sphere having a mesoporous structure of the present invention comprises the following steps: (A) providing a hollow sphere stencil having a mesoporous structure, wherein the hollow sphere stencil comprises: a first shell The body has a plurality of passages through the first casing, the material of the first casing comprises a regularly arranged mesoporous ceria material, and the pore arrangement of the mesoporous ceria material has a cubic symmetrical structure; (B) The hollow sphere stencil is mixed with a metal precursor; (C) the metal precursor is reduced; and (D) the hollow sphere stencil is removed to obtain a metal hollow sphere having a mesoporous structure.

Here, in the step (B), the metal precursor can penetrate into the mesopores through the capillary phenomenon, and then fill the hollow structure of the hollow sphere template. By adjusting the mixing ratio of the metal precursor to the hollow sphere stencil, the hollow structure of the hollow sphere stencil can be completely filled with the metal precursor. Further, in the step (B), the molten metal precursor can be directly used. If necessary, the metal precursor may also be dissolved in a solvent such as acetone, ethanol or the like to form a metal precursor solution.

Through the above process, the metal hollow sphere with the mesoporous structure of the present invention can be obtained, comprising: a second casing having a plurality of passages through the second casing, wherein the material of the second casing comprises a rule The mesoporous metal material is arranged, and the pore arrangement of the mesoporous metal material has a cubic symmetrical structure.

The cerium dioxide stencil used in the past has a pore structure, but is mostly a bulk material and does not have a hollow structure. Therefore, when a metal material having a hole structure is fabricated by a conventional stencil, there is often a problem of how to selectively fill a metal precursor into a hole. At the same time, because the metal precursor density is often much smaller than the reduced metal, even if the metal precursor can completely fill the hole, the reduced metal can only fill less than half of the hole volume. Even, even if the metal precursor is repeatedly filled and then subjected to a reduction reaction, it is impossible to produce a metal nanostructure having a complete replica stencil hole structure. In contrast, in the method for manufacturing a metal hollow sphere having a mesoporous structure according to the present invention, the metal precursor can be filled into the hollow structure of the hollow sphere stencil in addition to being filled in the hole of the casing. Therefore, in addition to the metal precursor in the casing hole can be reduced in the hole of the stencil casing, the metal precursor filled in the hollow structure of the hollow ball stencil can also be continuously filled into the hole of the stencil casing to enhance the reduction. The metal occupies a volume in the bore of the housing. Accordingly, the manufacturing method of the present invention can completely replicate the hollow sphere stencil structure and form a metal hollow sphere having the same structure as the hollow sphere stencil.

In addition, the metal hollow sphere obtained by the invention has a metal structure with a nanometer size (2.5-5 nm), so that a metal nanostructure of a metal hollow spherical shell is formed, which has a large reaction surface area. Accordingly, when the metal hollow sphere of the present invention is used as a catalyst, the catalytic efficiency can be improved. In addition, since the material generally used as a metal catalyst is a precious metal, it is often expensive. However, the metal hollow sphere of the present invention can be adjusted due to the pore size of the mesoporous structure and the thickness of the shell, so that the maximum reaction area can be obtained under the lowest precious metal precursor usage amount to optimize the catalytic efficiency.

In the method for fabricating a metal hollow sphere having a mesoporous structure according to the present invention, the hollow sphere template of the step (A) is prepared by the following steps: (A1) providing an alkaline aqueous solution of a surfactant, interface activity The alkaline aqueous solution comprises: a cationic surfactant, and a nonionic surfactant, wherein the cationic surfactant is represented by the following formula (I), and the nonionic surfactant is represented by the following formula (II):

Wherein R ₁ and R ₂ are each a C ₁ -C ₃ alkyl group, R ₃ is a C ₁₂ -C ₂₂ alkyl group, R ₄ is a C ₁₂ -C ₂₂ alkyl group, and n is an integer of 2 to 20 And (A2) adding a cerium oxide precursor to the surfactant solution to react the cerium oxide precursor into a hollow sphere template having a regular arrangement of mesoporous structures, and the cerium oxide precursor is as follows ( III):

Si(OR ₅ ) ₄ (III)

Wherein, each of R ₅ is independently a C ₁ -C ₃ alkyl group.

By the above process, a hollow sphere stencil having a special structure can be provided. Among them, by using a cationic surfactant and a nonionic surfactant, the ceria precursor can be self-assembled into a hollow sphere by a simple process. By adjusting the relative amounts of the components of the reaction solution and other reaction conditions, the outer diameter (i.e., particle diameter) and inner diameter of the hollow sphere and the thickness of the shell layer can be controlled. In addition, using the hollow spheres of the mesoporous structure regularly formed by the above method, the pore arrangement of the mesoporous ceria material has a cubic symmetrical structure, which is a bicontinuous passage through the casing.

In addition, in the method for fabricating a metal hollow sphere having a mesoporous structure according to the present invention, the hollow sphere stencil preferably has a hydrophobic surface.

In the metal hollow sphere having the mesoporous structure of the present invention and the manufacturing method thereof, preferably, the mesoporous ceria material of the hollow sphere template and the pore arrangement of the mesoporous metal material of the metal hollow sphere are arranged. The symmetrical structure is Ia3d.

In the step (A2) of the present invention, the amount of the ceria precursor is added in the range of 0.7 to 1 mol. Further, the reaction temperature of the ceria precursor is 25 to 50 °C.

In the cationic surfactant of the formula (I) of the present invention, it is preferred that R ₁ and R ₂ are each independently methyl, ethyl or propyl, and R ₃ is C ₁₄ to C _{20 .} alkyl. More preferably, R ₁ and R ₂ are each independently a methyl group or an ethyl group, and R ₃ is a C ₁₄ -C ₂₀ alkyl group. Most preferably, is a cationic surfactant-based N - cetyl - N, N - dimethylphenyl ammonium halides (N -hexadecyl- N, N -dimethylbenzenaminium halide ) ( Formula (IV)), N - benzyl yl - N, N - dimethyl hexadecyl ammonium halides -1- (N -benzyl- N, N -dimethylhexadecan- 1-aminium halide) ( formula (V)), or N, N - dimethyl - N ,N- dimethyl- N- phenethylhexadecan-1-aminium halide (formula (VI)), wherein the cationic surfactant can be monochloro Salt, or monobromide salt:

Further, in the nonionic surfactant represented by the formula (II) of the present invention, R ₄ is preferably a C ₁₄ to C ₂₀ alkyl group, and n is an integer of 2 to 10. More preferably, R ₄ is an alkyl group of C ₁₄ to C ₁₈ , and n is an integer of 2 to 5. Most preferably, R ₄ is an alkyl group of C ₁₆ and n is an integer of 2 to 3.

In the cerium oxide precursor represented by the formula (III) of the present invention, R ₅ may each independently be a C ₁ -C ₃ alkyl group. Preferably, each R ₅ is the same and is a methyl, ethyl, or propyl group. Most preferably, each R ₅ is an ethyl group. Here, a specific example of the cerium oxide precursor may be tetramethoxysilane (TMOS), Tetraethoxysilane (TEOS), or Tetrapropoxysilane (TPOS).

Further, in the step (A1) of the present invention, the alkaline aqueous solution of the surfactant comprises: 0.065 to 0.095 mol parts of a cationic surfactant, and 0.005 to 0.035 mol parts of a nonionic surfactant. Further, in the step (A1), the amount of the surfactant solution may be from 300 to 2000 moles. By adjusting the amount of water or the relative amount of each component of the reaction liquid, the outer diameter (i.e., particle diameter) and inner diameter, and thickness of the shell of the hollow sphere stencil can be controlled.

Furthermore, the alkaline aqueous solution of the surfactant of the step (A1) of the present invention may further comprise: an inorganic base. The inorganic base may be lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), barium hydroxide (RbOH), or ammonia water (NH ₄ OH). Preferably, the inorganic base is LiOH, NaOH, KOH, or NH ₄ OH. More preferably, the inorganic base is NaOH. Further, the amount of the inorganic base added is preferably from 0.1 to 0.5 mol parts. More preferably, the basic catalyst is added in an amount of from 0.25 to 0.4 moles.

In addition to the cerium oxide hollow sphere template described in the method for producing a metal hollow sphere having a mesoporous structure of the present invention, as described in Taiwan Patent Application No. 100110568 and US Patent Application No. 13/204,143 The structure, composition, and method of making the yttria hollow sphere are also incorporated herein by reference.

In the metal hollow sphere having the mesoporous structure of the present invention and the manufacturing method thereof, the material of the metal hollow sphere may be platinum, gold, silver, palladium, iron, cobalt, nickel, or an alloy thereof. Preferably, the material of the metal hollow sphere is platinum. The metal precursor may be a chlorate or a nitrate of platinum, gold, silver, palladium, iron, cobalt or nickel, such as chloroplatinic acid (H ₂ PtCl ₆ ) or nickel nitrate (Ni(NO ₃ ) ₂ ). Or other metal salts. Preferably, the metal precursor is chloroplatinic acid.

On the other hand, in the method for fabricating a metal hollow sphere having a mesoporous structure according to the present invention, in the step (C), a reduction technique known in the art can be selected according to the type of the metal precursor. Precursor. Preferably, in the step (C), hydrogen gas is introduced to reduce the metal precursor.

Further, in the method of fabricating a metal hollow sphere having a mesoporous structure of the present invention, in the step (D), any method of dissolving cerium oxide known in the art may be selected to remove the hollow sphere stencil. Preferably, in step (D), hydrofluoric acid (HF) is used to remove the hollow sphere stencil.

In the metal hollow sphere having a mesoporous structure of the present invention and the manufacturing method thereof, the particle diameter of the hollow sphere stencil is preferably 50-300 nm; and the thickness of the shell layer is preferably 5-50 nm. Due to the metal hollow sphere obtained by the invention, the structure and shape of the hollow sphere template can be completely reproduced, so the particle size and the thickness of the shell of the hollow metal sphere are the same as those of the hollow sphere template. Preferably, the metal hollow sphere has a particle size of 50-300 nm and a shell thickness of 5-50 nm.

Example Preparation of cerium oxide hollow sphere template

0.7 moles of cationic surfactant and 1200 moles of deionized water were added to the reaction flask and stirred at 35 ° C until dissolved. In the present embodiment, the cationic surfactant is a line N - benzyl - N, N - dimethyl hexadecyl ammonium chloride -1- (N -benzyl- N, N -dimethylhexadecan- 1-aminium chloride) .

To the mixture was added 0.3 mol of a nonionic surfactant and stirred at 35 ° C until dissolved. In this example, the nonionic surfactant is C ₁₆ H ₃₃ (OC ₂ H ₄ ) ₂ OH.

Then, 0.32 mol parts of an inorganic base was added to the aqueous solution containing the cationic surfactant and the nonionic surfactant, and stirred at 35 ° C until dissolved. In the present embodiment, the inorganic base is sodium hydroxide. Through the above steps, an alkaline aqueous solution of the surfactant can be obtained.

Then, a 1 molar portion of the ceria precursor was added to the alkaline aqueous solution of the surfactant, and the mixture was stirred at 35 ° C for 2 to 8 hours, and then aged at 70 to 90 ° C for 1 to 3 days. In this example, the ceria precursor used tetraethoxy decane (TEOS).

Finally, the reaction solution was filtered and dried to obtain a hollow sphere stencil of this example. The unbroken hollow sphere stencil is shown by a scanning electron microscope (SEM) by a transmission electron microscope (TEM) and a crushed hollow sphere stencil. The hollow sphere template of this embodiment is a hollow circle. The spheres have a particle size of about 150 nm, as shown in Figures 1 and 2.

In addition, the powder diffractometer signal of the X-ray diffraction (XRD) pattern confirmed that the hole arrangement structure symmetry of the mesoporous ceria hollow sphere template material of the present embodiment is Ia3d, as shown in FIG.

Preparation of platinum metal hollow spheres

1 gram of the cerium oxide hollow sphere prepared above was added to 50 ml of toluene (Toluene) and 1 ml of hexamethyldisilazane (Hexamethyldisilazane) for 0.5 to 1 hour, and the reaction solution was filtered and dried to prepare an outer layer. The surface is hydrophobized with a hollow sphere template.

The outer surface hydrophobicized ceria hollow sphere template prepared above was mixed with a platinum precursor (hollow sphere template: chloroplatinic acid = 0.1 g: 0.5834 g). In this example, the platinum precursor was solid H ₂ PtCl ₆ ‧6H ₂ O (100%). At 70 ° C, the solid chloroplatinic acid forms a molten state and passes through the capillary phenomenon, so that the platinum precursor solution penetrates into the pores of the hollow sphere stencil shell and completely fills the hollow structure of the hollow sphere stencil.

The platinum precursor is then reduced by the introduction of hydrogen. In this example, under hydrogen, the temperature was raised to 200 ° C at 0.75 ° C per minute, and after holding for 3 hours, the reduction was completed by cooling.

Finally, the above reactants were mixed with hydrofluoric acid (8%), and the hollow spheroidal stencil of cerium oxide was dissolved by hydrofluoric acid. After drying, the platinum metal hollow sphere of this example is obtained. At the same time, the crushed platinum metal hollow spheres were displayed by scanning electron microscopy (SEM) and unbroken platinum metal hollow spheres by transmission electron microscopy (TEM) (see Figure 4 and Figure 5). The metal hollow sphere of the present embodiment has a hollow structure 12, and the shell layer 11 does have a regular arrangement of mesopores 112, the schematic of which is shown in FIG. Further, the metal hollow sphere of the present embodiment has a particle diameter of about 150 nm.

The above-mentioned embodiments are merely examples for convenience of description, and the scope of the claims is intended to be limited to the above embodiments.

11. . . Shell

112. . . Mesopores

12. . . Hollow structure

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a transmission electron micrograph of a hollow sphere stencil of an embodiment of the present invention.

2 is a scanning electron micrograph of a crushed hollow sphere stencil according to an embodiment of the present invention.

3 is an X-ray diffraction pattern of a hollow sphere stencil according to an embodiment of the present invention.

4 is a transmission electron micrograph of a metal hollow sphere of an embodiment of the present invention.

Figure 5 is a scanning electron micrograph of a crushed metal hollow sphere in accordance with an embodiment of the present invention.

Fig. 6 is a schematic cross-sectional view showing a metal hollow sphere according to an embodiment of the present invention.

11. . . Shell

112. . . Mesopores

12. . . Hollow structure

Claims (22)

A method for manufacturing a metal hollow sphere having a mesoporous structure comprises the following steps: (A) providing a hollow sphere stencil having a mesoporous structure, wherein the hollow sphere stencil comprises: a first shell having a plurality The material of the first casing comprises a regularly arranged mesoporous ceria material, and the pore arrangement of the mesoporous ceria material has a cubic symmetrical structure; (B) The hollow sphere template is mixed with a metal precursor; (C) the metal precursor is reduced; and (D) the hollow sphere template is removed to obtain a metal hollow sphere having a mesoporous structure; wherein the hollow circle The ball stencil has a hydrophobic outer surface. The manufacturing method according to claim 1, wherein the cubic symmetrical structure is Ia3d. The manufacturing method of claim 1, wherein the metal hollow sphere having a mesoporous structure comprises: a second housing having a plurality of passages extending through the second housing, the second housing The material comprises a regularly arranged mesoporous metal material, and the pore arrangement of the mesoporous metal material has a cubic symmetrical structure. The manufacturing method according to claim 3, wherein the cubic symmetrical structure is Ia3d. The manufacturing method according to claim 1, wherein the hollow sphere template of the step (A) is prepared by the following steps: (A1) providing an alkaline aqueous solution of a surfactant, the surfactant base The aqueous solution comprises: a cationic surfactant, and a nonionic surfactant, wherein the cationic surfactant is represented by the following formula (I), and the nonionic surfactant is represented by the following formula (II): And R ₄ -(OC ₂ H ₄ ) _n -OH(II); wherein R ₁ and R ₂ are each C ₁ -C ₃ alkyl, R ₃ is C ₁₂ -C ₂₂ alkyl, R ₄ is a C ₁₂ -C ₂₂ alkyl group, n is an integer from 2 to 20; and (A2) a cerium oxide precursor is added to the surfactant solution to react the cerium oxide precursor into a regular arrangement A hollow sphere stencil of a mesoporous structure, and the cerium oxide precursor is represented by the following formula (III): Si(OR ₅ ) ₄ (III) wherein each of the R ₅ groups is independently a C ₁ -C ₃ alkyl group. The preparation method of claim 5, wherein the alkaline aqueous solution of the surfactant further comprises: an inorganic base. The production method according to claim 6, wherein the inorganic base is selected from the group consisting of LiOH, NaOH, KOH, RbOH, and NH ₄ OH. The production method according to Item 5, wherein R ₁ and R ₂ are each independently a methyl group or an ethyl group, and R ₃ is a C ₁₄ -C ₂₀ alkyl group. The production method according to claim 8, wherein the cationic surfactant is selected from the group consisting of the following formulas (IV), (V), and (VI): ,and The production method according to claim 5, wherein R ₄ is a C ₁₄ to C ₂₀ alkyl group, and n is an integer of 2 to 10. The production method according to claim 10, wherein R ₄ is a C ₁₆ alkyl group, and n is an integer of 2 to 5. The production method of claim 5, wherein each R ₅ is a methyl group, an ethyl group, or a propyl group. The manufacturing method according to claim 1, wherein the material of the metal hollow sphere is platinum, gold, silver, palladium, iron, cobalt, nickel or an alloy thereof. The production method according to claim 1, wherein the metal precursor is platinum, gold, silver, palladium, iron, cobalt or nickel metal salts. The production method according to claim 1, wherein in the step (C), hydrogen gas is introduced to reduce the metal precursor. The production method according to claim 1, wherein in the step (D), hydrofluoric acid (HF) is used to remove the hollow sphere stencil. The production method according to claim 1, wherein the hollow sphere template has a particle diameter of 50 to 300 nm. The production method according to claim 1, wherein the metal hollow sphere has a particle diameter of 50 to 300 nm. A metal hollow sphere having a mesoporous structure, comprising: a second casing having a plurality of passages extending through the second casing, wherein the material of the second casing comprises a regularly arranged mesoporous metal material, and the The pore arrangement of the mesoporous metal material has a cubic symmetrical structure. The metal hollow sphere according to claim 19, wherein the cubic symmetrical structure is Ia3d. The metal hollow sphere according to claim 19, wherein the material of the metal hollow sphere is platinum, gold, silver, palladium or an alloy thereof. The metal hollow sphere according to claim 19, wherein the metal hollow sphere has a particle size of 50-300 nm.