Double hollow structure yolk-shell nanoparticle

Abstract

The present invention addresses the problem of providing a yolk-shell nanoparticle that can function as a photocatalyst capable of using not only ultraviolet light and visible light but also near-infrared light, and that can produce hydrogen with high efficiency.　The problem is solved by a double hollow structure yolk-shell nanoparticle comprising: a first outer shell part; a first hollow part formed in the first outer shell part; and a hollow gold nanoparticle present in the first hollow part and composed of a second outer shell part and a second hollow part formed in the second outer shell part, wherein the hollow gold nanoparticle has a diameter of the second hollow part of 30-100 nm and a thickness of the second outer shell part of 2-10 nm, and the first outer shell part is composed of a metal sulfide and / or a metal oxide.

Description

Double hollow yolk-shell nanoparticles

[0001] The present invention relates to yolk-shell nanoparticles that function as photocatalysts and can utilize not only ultraviolet and visible light but also near-infrared light.

[0002] Since the Industrial Revolution in the 18th century, fossil fuels have been used as the main energy source. Mass consumption of these fossil fuels has increased carbon dioxide in the atmosphere, which is thought to have contributed to global warming. From the perspective of resolving current global environmental issues and future energy problems that support the sustainable development of the Earth, there is a need to develop technologies that can obtain chemical fuels such as hydrogen from reusable resources such as water and biomass.

[0003] Photocatalysts are used to convert solar energy from water, biomass, etc. into chemical energy such as hydrogen. To date, a method has been proposed for producing hydrogen from organic matter by irradiating a photocatalyst such as titanium oxide with ultraviolet light (see Non-Patent Document 1). However, ultraviolet light accounts for only about 6% of the energy density of natural light, and visible light, which accounts for about half of the energy density of natural light, has not been effectively utilized. Therefore, a photocatalyst that can effectively utilize visible light has been desired.

[0004] Therefore, a composite in which cuprous oxide is supported on a clay mineral has been proposed as a photocatalyst that can efficiently and stably produce hydrogen using organic materials as raw materials under irradiation with visible light (400 to 600 nm) (see Patent Document 1).

[0005] As a result, by using visible light, it has become possible to expand the range of use of natural light by combining it with ultraviolet light, but the remaining near-infrared light of natural light cannot be utilized. Therefore, to further improve efficiency, a photocatalyst that can effectively utilize near-infrared light is required, and in recent years, photocatalysts that can effectively utilize near-infrared light have been reported (see Non-Patent Documents 2, 3, and 4).

[0006] Patent No. 5548934

[0007] Didler Robert, Catalyst Today 122 (2007) 20-26ACS Appl. Mater. Interfaces 2022,14, 48967-48975J. Am. Chem. Soc. 143, 19567-19575 (2021)Nature Communications (2024) 15:413

[0008] As described above, photocatalysts that can effectively utilize near-infrared light have been reported. However, the substances used in Non-Patent Documents 2 and 3 are both chalcogen compounds of lead or mercury, which are toxic and have stability issues. Furthermore, although the technology of Non-Patent Document 4 solves the issues of toxicity and stability, further improvement in hydrogen production efficiency is required for practical use. The present disclosure provides a new photocatalyst that can utilize not only ultraviolet and visible light but also near-infrared light, and that can efficiently and stably produce hydrogen under natural light irradiation.

[0009] As a result of intensive research to solve the above problems, the present inventors have discovered that double hollow york-shell nanoparticles with a novel configuration are photocatalysts that can utilize not only ultraviolet and visible light but also near-infrared light, and that can produce hydrogen with high efficiency. Based on this finding, the present inventors have further developed the present invention and completed the present invention. This disclosure includes the following inventions.

[0010] [1] A double hollow york-shell nanoparticle comprising a first outer shell, a first hollow portion formed within the first outer shell, and a hollow gold nanoparticle present within the first hollow portion and comprising a second outer shell and a second hollow portion formed within the second outer shell, wherein the diameter of the second hollow portion is 30 nm to 100 nm and the thickness of the second outer shell is 2 nm to 10 nm, and the first outer shell is composed of a metal sulfide and / or a metal oxide. [2] The double hollow york-shell nanoparticle according to [1], wherein the diameter of the first hollow portion is 50 nm to 300 nm and the thickness of the first outer shell is 10 nm to 50 nm. [3] The double hollow york-shell nanoparticle according to [1] or [2], wherein the first outer shell is composed of any component selected from the group consisting of cadmium sulfide, zinc sulfide, nickel sulfide, and copper sulfide.

[0011] The present disclosure provides yolk-shell nanoparticles that function as photocatalysts that can utilize not only ultraviolet and visible light but also near-infrared light and that can produce hydrogen with high efficiency. By using the yolk-shell nanoparticles of the present disclosure, it is possible to efficiently produce hydrogen from resources such as water and biomass, particularly by utilizing solar (natural light) energy.

[0012] Schematic cross-sectional view of double hollow york-shell nanoparticles. TEM image (photograph substitute for drawing) of synthesized hollow gold nanoparticles. (a) and (b) are both TEM images (photograph substitute for drawing) of synthesized double hollow york-shell CdS nanoparticles. TEM images (photograph substitute for drawing) of synthesized gold nanoparticle york-shell CdS nanoparticles. TEM image (photograph substitute for drawing) of synthesized shell-type CdS nanoparticles. Graph showing the results of hydrogen production using the photocatalyst of the example. Graph showing the results of hydrogen production using the photocatalyst of the example and comparative example.

[0013] One embodiment of the present disclosure is a double hollow structure yolk-shell nanoparticle. The yolk-shell structure, also known as an egg-yolk structure, is a structure in which particles are encapsulated in a hollow space inside an outer shell. This embodiment is a double hollow structure in which the internal particles present in the hollow space are also hollow. Specifically, the nanoparticle is composed of a first outer shell, a first hollow space formed within the first outer shell, and a hollow gold nanoparticle present within the first hollow space and consisting of a second outer shell and a second hollow space formed within the second outer shell.

[0014] The hollow gold nanoparticles have a diameter of the second hollow portion of 30 nm to 100 nm, and a thickness of the second outer shell of 2 nm to 10 nm. The first outer shell is composed of a metal sulfide and / or a metal oxide. This configuration enables the nanoparticles to be used as photocatalysts that can utilize light energy not only in the ultraviolet and visible ranges but also in the near-infrared range (wavelengths of 600 nm or greater), particularly using sunlight (natural light) energy to efficiently produce hydrogen from resources such as water and biomass.

[0015] Figure 1 is a cross-sectional schematic diagram of a yolk-shell nanoparticle 10 with a double hollow structure. Hatching in the figure indicates the outer shell portion, and unhatched areas indicate the hollow portion. The yolk-shell nanoparticle 10 consists of a first outer shell portion 1, a first hollow portion 2 formed therein, and a hollow gold nanoparticle 11 present in the first hollow portion. The hollow gold nanoparticle 11 consists of a second outer shell portion 3 and a second hollow portion 4 formed therein.

[0016] The diameter of the first hollow portion 2 is not particularly limited, but is preferably 50 nm or more, more preferably 60 nm or more, in order to utilize light scattering. Furthermore, in terms of the specific surface area for reaction, it is preferably 300 nm or less, more preferably 200 nm or less. The thickness of the first outer shell portion 1 is not particularly limited, but is preferably 10 nm or more, more preferably 15 nm or more. Furthermore, it is preferably 50 nm or less, more preferably 30 nm or less. When the thickness of the first outer shell portion 1 is within the above range, excitons are generated efficiently.

[0017] The diameter of the second hollow portion 4 of the hollow gold nanoparticle 11 is 30 nm or more and 100 nm or less, preferably 40 nm or more and 80 nm or less. The thickness of the second outer shell portion 3 is not particularly limited, but is 2 nm or more and 10 nm or less, preferably 3 nm or more and 8 nm or less. When the thickness of the second outer shell portion 3 is within the above range, excitons are generated efficiently. Note that in the cross-sectional schematic diagram of FIG. 1 , the second outer shell portion 3 of the hollow gold nanoparticle 11 is not in contact with the first outer shell portion 1, but the second outer shell portion 3 of the hollow gold nanoparticle 11 may be in contact with the first outer shell portion 1.

[0018] The diameter of the hollow portion and the thickness of the outer shell portion can be measured from SEM images or TEM images. The diameter of the hollow portion is taken as the median value of the maximum and minimum diameters in the image. The thickness of the outer shell portion is taken as the median value of the maximum and minimum thicknesses in the image.

[0019] The synthesis method of hollow gold nanoparticles is not particularly limited, but a general technique used to synthesize hollow structures, such as a template method, can be used. ｘ B ｙ Co-based particles are susceptible to oxidation, and Co ２＋ Co / Co is commonly used to fabricate hollow structures due to its rather negative reduction potential (E0 = -0.277 V vs. SHE). ｘ B ｙ The scaffold is HAuCl ４ When exposed to AuCl ４ － The reduction potential of Co ２＋ Since the Au is higher than the Co ｘ B ｙ As a result, the core becomes Co ｘ B ｙ The shell is then coated with Au to form a nanostructure. ｘ B ｙ The core is oxidatively etched by air, leaving only the outer Au shell.

[0020] Alternatively, hollow gold nanoparticles can be synthesized using silver nanoparticles as scaffolds. In this case, it is preferable to synthesize the gold nanoparticles so that the gold / silver ratio is 25% by weight or more.

[0021] The first outer shell 1 is composed of a metal sulfide and / or a metal oxide. Examples of metal sulfides include cadmium sulfide, zinc sulfide, nickel sulfide, copper sulfide, molybdenum sulfide, mercury sulfide, iron sulfide, and lead sulfide. Examples of metal oxides include cadmium oxide, zinc oxide, nickel oxide, copper oxide, titanium oxide, aluminum oxide, silicon oxide, and tungsten oxide. The first outer shell 1 may contain other substances as long as the effects of the present disclosure are not impaired. Examples of other substances include metal impurities, organic impurities, and inorganic impurities.

[0022] The synthesis method of the first outer shell portion 1 is not particularly limited, but a synthesis method utilizing the Kirkendall effect can be used. ２ O (Ksp = 2 × 10 －１５ ) and Cu ７ S ４ (Ksp = 1 x 10 －４８ ) by utilizing the difference in solubility of Cu ２ O to Na ２ When S is introduced, Cu ２ O spontaneously dissolves in Cu. ７ S ４ Furthermore, S ２－ Cu ions diffuse outwards ２＋ Cu ions diffuse inwards more slowly than Cu ions. ２ O and Cu ７ S ４ By utilizing this nanoscale Kirkendall effect, a hollow Cu ７ S ４ is first synthesized. Then, Cu is added as needed. ２ In order not to destroy the original morphology of O, Cu ７ S ４ is replaced by a metal sulfide such as cadmium sulfide, copper sulfide, or nickel sulfide, or a metal oxide.

[0023] In addition to the above-mentioned Kirkendall effect, synthesis may also be carried out by methods such as Ostwald ripening, heat treatment, chemical etching, and galvanic exchange.

[0024] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. ２ B) Synthesis of NP scaffolds ２ The BNP scaffold uses citrate as the capping ligand and NaBH ４ by Co ２＋ Synthesized by ionic nucleation. 0.40 mM CoCl ２ ・6H ２ O and 4.0 mM Na ３ C ６ H ５ O ７ ・2H ２ A 100 mL solution of 1M NaBH2O was prepared in a 500 mL round-bottom flask and degassed by bubbling nitrogen for 1 hour. During this time, the solution was stirred at 700 rpm using a magnetic stir bar. Then, while the solution was kept stirring under nitrogen protection, a predetermined amount of freshly prepared 1M NaBH2O was added. ４ An aqueous solution (25-200 μL) was injected. ４ After the addition of Co, the solution turned from pale pink to brown. ２＋ ions are reduced, and Co ２ The formation of BNP scaffolds was confirmed. After 2 min, a stirring bar was magnetically suspended above the solution, followed by Co ２ The BNPs were left under a constant nitrogen flow for 2 hours to completely hydrolyze any residual borohydride nucleating agent.

[0025] (Co ２ B) Control of NP diameter) Larger Co ２ To synthesize BNPs, a certain amount of B(OH) ４－ (20-200 μL) freshly prepared 1 M NaBH ４ The B(OH) solution was added to the aqueous solution and mixed quickly before being poured into the cobalt salt solution. ４－ The onset of the color change from pale pink to brown / gray was prolonged by B(OH). ４－ To obtain 1.0 M NaBH ４1.0 mL aliquots of the aqueous solution were prepared and allowed to hydrolyze under these conditions for 48 hours.

[0026] (Synthesis of hollow gold nanoparticles) Chloroauric acid (HAuCl ４ ) was purchased from Fisher Scientific. All water used in the synthesis was ultra-pure and had a resistivity of 18.3 MΩ. Using the anaerobic galvanic effect (GE), a predetermined amount (1.00-10.0 μL) of 0.10 M HAuCl ４ was added to 15 mL of ultrapure water and degassed by bubbling nitrogen gas for 1 hour with magnetic stirring at 700 rpm. After degassing, 15 mL of Co was added via air-free cannula transfer. ２ Galvanic exchange (GE) was initiated by transferring the B NP solution into the stirring gold solution. ２ B NP / Au (core / shell) particles were stirred at 700 rpm for 2 minutes under nitrogen protection, and then the remaining Co ２ The B NP core was fully oxidized. The remaining cobalt core was fully oxidized by removing the septum, stirring at 700 rpm for 3 minutes under the same conditions, and then transferring a 3.0 mL aliquot to a vial and vortexing for 10 seconds. For aerobic GE, a predetermined amount (1.00-10.0 μL) of 0.10 M HAuCl was added. ４ was added to 15 mL of ultrapure water and stirred for 60 minutes under conditions consistent with the anaerobic protocol. ２ GE was initiated by transferring the B NP solution into the stirring gold solution. ２ B NP / Au (core / shell) particles were stirred at 700 rpm for 5 minutes under these conditions to remove residual Co. ２ The BNP core was fully oxidized.

[0027] The resulting hollow gold nanoparticles (HGNs) had a hollow spherical morphology with a core size of 42±4 nm and a shell thickness of 6±1 nm. As can be seen from the TEM image shown in Figure 2, the HGNs had a hollow structure.

[0028] Example 1 (HGN / Cu２ Fabrication of Cu (core / shell) nanoparticles: Using a citrate reduction approach, HGN particles with an average diameter of approximately 45 nm were obtained. ２ To deposit O, a predetermined amount of NaOH solution (1.5 mL, 1.0 M) was added to deionized water (32.5 mL), followed by CuSO. ４ The solution (4.0 mL, 0.01 M), Au colloid (3.0 mL, 0.25 mM), and L-ascorbic acid (0.5 mL, 0.1 M) were added sequentially. The mixture was stirred at 35°C for 10 minutes, and the product HGN / Cu was obtained. ２ O was purified with deionized water and collected by centrifugation.

[0029] (HGN / Cu ７ S ４ Preparation of yolk-shell nanoparticles) The above-obtained HGN / Cu ２ Methanol colloid (0.4 mmol, 10.0 mL) was dissolved in Na ２ The product (HGN / Cu) was mixed with 0.2 M S solution (800 μL) under vigorous stirring for 10 minutes. ７ S ４ ) was washed with HCl solution (pH=10) and collected by centrifugation.

[0030] (Preparation of HGN / CdS yolk-shell nanoparticles) ７ S ４ Methanol colloid (0.4 mmol, 10.0 mL) was added to a 50 mL flask, followed by Cd(NO ３ ) ２ ・4H ２ To the mixture was added 0 (4 mmol in 1.5 mL of methanol) and tributyl phosphate (TBP) (8 mmol in 1.0 mL of toluene). The mixture was heated at 50°C with stirring for 12 hours. The product (HGN / CdS) was collected by centrifugation and dispersed in methanol for subsequent analysis.

[0031] Figures 3(a) and (b) show TEM images of HGN / CdS yolk-shell nanoparticles with a double hollow structure. The thickness of the CdS shell (first outer shell) was (a) 18±3 nm and (b) 25±3 nm. The diameter of the hollow portion was (a) 160±9 nm and (b) 164±11 nm.

[0032] Comparative Example 1 (Preparation of Au / CdS yolk-shell nanoparticles) Au / CdS yolk-shell nanoparticles were synthesized in the same manner as in Example 1, except that gold nanoparticles (diameter 44±6 nm) were used instead of HGN. A TEM image of the resulting Au / CdS yolk-shell nanoparticles is shown in Figure 4. The thickness of the CdS shell was 22±3 nm. The TEM images of the examples and comparative examples were taken with a high-resolution transmission electron microscope (HRTEM, JEOL, JEM-ARM200FTH).

[0033] (Evaluation of hydrogen generation by photocatalysis) ２ The generation was carried out under visible and near-infrared light (λ = 400-700 nm). 3.4 × 10 sample particles were added to 27 mL of pure water in a beaker. １１ In addition, 90 mW / cm ２ The amount of hydrogen generated was measured by irradiating the nanoparticles with light of wavelengths of 400 to 700 nm using a xenon lamp (LCS-100, 94011A, Newport) operating at 400°C. As shown in Figure 6, the two double hollow HGN / CdS yolk-shell nanoparticles shown in Figures 3(a) and 3(b) produced significantly more hydrogen than the pure hollow CdS nanoparticles shown in Figure 5 and the pure HGN nanoparticles shown in Figure 2. ２ The production yield increased dramatically, demonstrating that the synergistic interaction between HGN and CdS enhances the photocatalytic activity.

[0034] Furthermore, by comparing the activity of the double hollow york-shell nanoparticles prepared in Example 1 with that of the single hollow york-shell nanoparticles prepared in Comparative Example 1, it was found that H ２ The double hollow yoke-shell nanoparticles were found to be superior in terms of production yield (Figure 7), demonstrating that the hollow structure of the plasmonic metal yoke can be used to improve photocatalytic efficiency.

[0035] [Additional remarks] The double hollow york-shell nanoparticles disclosed herein can be used as a highly efficient photocatalyst for hydrogen production, contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs). Goal 9: "Build resilient infrastructure for industry, innovation and sustainable development."

[0036] Although the present invention will be described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

[0037] 10 yolk-shell nanoparticle 11 hollow gold nanoparticle 1 first outer shell portion 2 first hollow portion 3 second outer shell portion 4 second hollow portion

Claims

1. A double hollow structure york-shell nanoparticle comprising: a first outer shell; a first hollow portion formed within the first outer shell; and a hollow gold nanoparticle present within the first hollow portion and consisting of a second outer shell and a second hollow portion formed within the second outer shell, wherein the diameter of the second hollow portion of the hollow gold nanoparticle is 30 nm or more and 100 nm or less, and the thickness of the second outer shell is 2 nm or more and 10 nm or less, and the first outer shell is composed of metal sulfide and / or metal oxide.

2. The double hollow york-shell nanoparticle according to claim 1, wherein the diameter of the first hollow portion is 50 nm or more and 300 nm or less, and the thickness of the first outer shell portion is 10 nm or more and 50 nm or less.

3. The double hollow structure york-shell nanoparticles according to claim 1 or 2, wherein the first outer shell portion is composed of any component selected from the group consisting of cadmium sulfide, zinc sulfide, nickel sulfide, and copper sulfide.

Images