Double hollow yoke-shell nanoparticles

Abstract

To provide a yoke-shell type nanoparticle which functions as a photocatalyst capable of utilizing not only ultraviolet light and visible light but also near-infrared light and can produce hydrogen with high efficiency.SOLUTION: Hollow gold nanoparticles each including a first outer shell portion, a first hollow portion formed in the first outer shell portion, a second outer shell portion, and a second hollow portion formed in the second outer shell portion, wherein diameters of the second hollow portions are 30nm or more and 100nm or less, and thicknesses of the second outer shell portions are 2nm or more and 10nm or less, wherein the first outer shell portion is composed of a metal sulfide and / or a metal oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[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 the amount of carbon dioxide in the atmosphere, which has led to global warming. It is believed that the current global environmental problems and the future of sustainable development of the earth From the perspective of solving energy problems, there is a need to develop technologies to obtain chemical fuels such as hydrogen from recyclable 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, while this technology can expand the range of natural light utilization by combining visible light with ultraviolet light, it does not utilize the remaining near-infrared light of natural light. 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). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5548934 [Non-patent literature]

[0007] [Non-Patent Document 1] Didler Robert, Catalyst Today 122 (2007) 20-26 [Non-patent document 2] ACS Appl. Mater. Interfaces 2022,14, 48967-48975 [Non-patent document 3] J. Am. Chem. Soc. 143, 19567-19575 (2021) [Non-patent document 4] Nature Communications (2024) 15:413 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned 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 have issues with toxicity and stability. Furthermore, although the technology in Non-Patent Document 4 solves the issues of toxicity and stability, further improvement in hydrogen generation 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. [Means for solving the problem]

[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 it. This disclosure includes the following inventions.

[0010] [1] A first outer shell portion; a first hollow portion formed in the first outer shell portion; a hollow gold nanoparticle present in the first hollow portion and comprising a second outer shell portion and a second hollow portion formed within the second outer shell portion; It consists of The hollow gold nanoparticle has a diameter of the second hollow portion of 30 nm or more and 100 nm or less, and a thickness of the second outer shell portion of 2 nm or more and 10 nm or less, The double hollow yolk-shell nanoparticles have a first outer shell made of a metal sulfide and / or a metal oxide. [2] The double hollow structure york-shell nanoparticle according to [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 york-shell nanoparticles according to [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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0012] [Figure 1]Schematic cross-sectional view of a double hollow yolk-shell nanoparticle. [Figure 2] TEM image of the synthesized hollow gold nanoparticles (photograph instead of drawing). [Figure 3] TEM image (photograph substitute for drawing) of the synthesized double hollow yolk-shell type CdS nanoparticles. [Figure 4] TEM image of synthesized gold nanoparticles and yolk-shell type CdS nanoparticles (photograph instead of drawing). [Figure 5] TEM image of the synthesized shell-type CdS nanoparticles (photograph instead of drawing). [Figure 6] Graph showing the results of hydrogen production using the photocatalyst of the example. [Figure 7] 6 is a graph showing the results of photocatalytic hydrogen production in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[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, it is composed of a first outer shell portion, a first hollow portion formed within the first outer shell portion, and a hollow gold nanoparticle that exists within the first hollow portion and consists of a second outer shell portion and a second hollow portion formed within the second outer shell portion.

[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 portion of 2 nm to 10 nm. The first outer shell portion is made of metal sulfide and / or metal oxide. By having such a structure, the purple gold nanoparticles can be obtained. It can be used as a photocatalyst that can utilize light energy not only in the visible range but also in the near-infrared range (wavelengths of 600 nm or more), and in particular, can utilize sunlight (natural light) energy to efficiently produce hydrogen from resources such as water and biomass.

[0015] 1 is a cross-sectional schematic diagram of a yolk-shell nanoparticle 10 with a double hollow structure. In the figure, hatching indicates the outer shell portion, and non-hatching indicates the hollow portion. The yolk-shell nanoparticle 10 comprises a first outer shell 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 comprises a second outer shell 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 terms of utilizing light scattering, and is preferably 300 nm or less, more preferably 200 nm or less, in terms of the reactive specific surface area. 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. Also, 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 preferably 80 nm or less. The thickness of the second outer shell 3 is not particularly limited, but is in the range of 2 nm to 10 nm, preferably 3 nm or more, and preferably 8 nm or less. When the thickness of the second outer shell 3 is in the above range, excitons are generated efficiently. In the cross-sectional view of FIG. 1, the second shell 3 of the hollow gold nanoparticle 11 is not in contact with the first shell 1, but the hollow gold nanoparticle 11 may be in contact with the first shell 1.

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

[0019] The method for synthesizing hollow gold nanoparticles is not particularly limited, but general techniques used for synthesizing hollow structures, such as template methods, can be used. For example, Co x B y Co-based particles are weak to oxidation, and Co 2+ Due to the rather negative reduction potential of Co / Co (E0 = -0.277 V vs. SHE), it is commonly used to fabricate hollow structures. x B y When the scaffold is exposed to HAuCl4, AuCl4 - Co 2+ Therefore, Au is replaced by Co by electrical substitution. x B y As a result, the core becomes Co x B y The shell is then formed into a nanostructure of Au. x B y The core is oxidatively etched away by air, leaving only the outer Au shell.

[0020] Alternatively, hollow gold nanoparticles can be synthesized using silver nanoparticles as a scaffold. 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, while 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 they do not impair the effects of the present disclosure. The other substances may include metal impurities, organic impurities, inorganic impurities, and the like.

[0022] The method for synthesizing the first outer shell portion 1 is not particularly limited, but a synthesis method utilizing the Kirkendall effect may be used. Specifically, the Kirkendall effect can be utilized in Cu2O (Ksp=2×10 -15 ) and Cu7S4 (Ksp=1×10 -48 ) by utilizing the difference in solubility of Na in CuO. When 2S is introduced, Cu2O spontaneously transforms into Cu7S4. 2- Cu ions diffuse outwards 2+ Because atoms diffuse inward more slowly than ions, voids form between the Cu2O and Cu7S4. Hollow Cu7S4 was first synthesized by utilizing this nanoscale Kirkendall effect. Then, if necessary, the CuO is replaced with a metal sulfide such as cadmium sulfide, copper sulfide, or nickel sulfide, or a metal oxide, without destroying the original morphology of the CuO.

[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. [Example]

[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. <Synthesis Example 1> (Synthesis of Co2B NP scaffold) The Co2B NP scaffold uses citrate as a capping ligand and NaBH4 as a capping ligand for Co 2+ A 100 mL solution of 0.40 mM CoCl 6H O and 4.0 mM Na C H O 2H O was prepared in a 500 mL round-bottom flask and degassed by bubbling nitrogen through it 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 1 M NaBH4 aqueous solution (25-200 μL) was injected. After the addition of NaBH4, the solution turned from pale pink to brown, indicating that Co2+ The reduction of ions confirmed the formation of the Co2B NP scaffold. After 2 min, a stir bar was magnetically suspended above the solution, and the Co2B NPs were then left under a constant nitrogen flow for 2 h to completely hydrolyze the residual borohydride nucleating agent.

[0025] (Control of Co2B NP diameter) To synthesize larger Co2B NPs, a certain amount of B(OH) 4- (20-200 μL) was added to a freshly prepared 1 M NaBH4 aqueous solution before injection into the cobalt salt solution. The mixture was quickly mixed with B(OH) 4- The onset of the color change from pale pink to brown / gray was prolonged by B(OH) 4- To obtain 1.0 mL aliquots of 1.0 M aqueous NaBH4 were prepared and allowed to hydrolyze under these conditions for 48 hours.

[0026] (Synthesis of hollow gold nanoparticles) Chloroauric acid (HAuCl4) was purchased from Fisher Scientific. All water used in the synthesis was ultrapure, with a resistivity of 18.3 MΩ. Anaerobic galvanic exchange (GE) was employed by adding a predetermined amount (1.00–10.0 μL) of 0.10 M HAuCl4 to 15 mL of ultrapure water and degassing it by bubbling nitrogen gas through it for 1 hour while magnetically stirring at 700 rpm. After degassing, galvanic exchange (GE) was initiated by transferring 15 mL of Co2B NP solution into the stirring gold solution via air-free cannula transfer. The resulting Co2B NP / Au (core / shell) particles were stirred at 700 rpm for 2 minutes under nitrogen protection, after which the remaining Co2B NP core was completely oxidized. The septum was removed and the mixture was stirred at 700 rpm for 3 minutes under these conditions, and a 3.0 mL aliquot was transferred to a vial and vortexed for 10 seconds to complete the oxidation. For GE, a predetermined amount (1.00–10.0 μL) of 0.10 M HAuCl was added to 15 mL of ultrapure water and stirred for 60 min under conditions consistent with the anaerobic protocol. GE was initiated by transferring 15 mL of Co2B NP solution into the stirring gold solution via cannula transfer in air. The obtained Co2B NP / Au (core / shell) particles were mixed under the same conditions at 700 rpm. The mixture was stirred at RT for 5 min to completely oxidize the residual Co2B NP cores.

[0027] The resulting hollow gold nanoparticles (HGNs) had a hollow spherical morphology with a core diameter 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 hollow structure of the HGNs was clearly observed.

[0028] Example 1 (Preparation of HGN / CuO (core / shell) nanoparticles) Using the citrate reduction approach, HGN particles with an average diameter of approximately 45 nm were obtained. To deposit CuO, a predetermined amount of NaOH solution (1.5 mL, 1.0 M) was added to deionized water (32.5 mL), followed by the sequential addition of CuSO4 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). The mixture was stirred at 35 °C for 10 min, and the resulting HGN / CuO was purified with deionized water and collected by centrifugation.

[0029] (Preparation of HGN / Cu7S4 yolk-shell nanoparticles) The obtained HGN / CuO methanol colloid (0.4 mmol, 10.0 mL) was mixed with NaS solution (0.2 M, 800 μL) under vigorous stirring for 10 min. The product (HGN / CuS) was washed with HCl solution (pH = 10) and collected by centrifugation.

[0030] (Preparation of HGN / CdS yolk-shell nanoparticles) The above-obtained HGN / Cu7S4 methanol colloid (0.4 mmol, 10.0 mL) was added to a 50 mL flask, followed by Cd(NO3)2 4H2O (1.5 mL of methanol). Tributyl phosphate (TBP) (8 mmol in 1.0 mL of toluene) was added and the mixture was heated at 50°C for 12 hours with stirring. / 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 using the same method 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 using a high-resolution transmission electron microscope (HRTEM, Japan The images were taken using a microscope (Electronics, JEM-ARM200FTH).

[0033] (Evaluation of photocatalytic hydrogen production) Photocatalytic H2 generation was performed 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 Plus 90mW / cm 2The amount of hydrogen generated was measured by irradiating the nanoparticles with light of wavelengths 400 to 700 nm using a xenon lamp (LCS-100, 94011A, Newport) operated at 400°C. As shown in Figure 6, the two double hollow HGN / CdS yolk-shell nanoparticles shown in Figure 3(a) and (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, a comparison of the activity of the double hollow yoke-shell nanoparticles prepared in Example 1 and the single hollow yoke-shell nanoparticles prepared in Comparative Example 1 shows that the double hollow yoke-shell nanoparticles are superior in terms of H2 production yield (Figure 7). This result supports the idea that photocatalytic efficiency can be improved by utilizing the hollow structure of the plasmonic metal yoke.

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

[0036] 10. Yolk-shell nanoparticles 11 Hollow gold nanoparticles 1 First outer shell 2 First hollow part 3 Second outer shell 4 Second hollow part

Claims

1. A first outer shell portion; a first hollow portion formed in the first outer shell portion; a hollow gold nanoparticle present in the first hollow portion and comprising a second outer shell portion and a second hollow portion formed within the second outer shell portion; It consists of The hollow gold nanoparticle has a diameter of the second hollow portion of 30 nm or more and 100 nm or less, and a thickness of the second outer shell portion of 2 nm or more and 10 nm or less, The double hollow yolk-shell nanoparticles have a first outer shell made of a metal sulfide and / or a metal oxide.

2. 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. 3. The double hollow structure york-shell nanoparticle according to claim 1, 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.

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