JP4076409B2 - Method for producing gold cobweb-like structure, gold cobweb-like structure, method for producing composite metal nanoparticles, and composite metal nanoparticles - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a gold cobweb-like structure, a gold cobweb-like structure, a method for producing a composite metal nanoparticle, and a composite metal nanoparticle.
[0002]
[Prior art]
Metal clusters and nanoparticles are attracting attention due to their chemical and physical properties depending on their size. For example, gold does not exhibit catalytic properties in the bulk, but gold nanoparticles on titanium oxide catalyze the oxidation reaction of CO under a low temperature of 200 K when the diameter is 10 nm or less. Further, it is known as a physical property of gold nanoparticles that light is emitted strongly when the size is smaller. In addition, it is also known that the melting point of gold nanoparticles rapidly decreases when the diameter becomes 5 nm or less.
[0003]
Thus, in addition to having the above properties, gold nanoparticles are expected to have unknown reactivity and physical properties. Furthermore, application to nanodevices such as molecular devices and nanofunctional devices is expected by utilizing the properties unique to gold nanoparticles.
[0004]
As for gold nanoparticles, for example, Takagi, M., J. Phys. Soc. Jpn., 9 (1954), 359. (Non-patent Document 1) and Buffat, DA, and Borel, JP, Phys. Rev. ., A13 (1976), 2289. (Non-patent Document 2).
[0005]
The production of ultrafine particles using a laser is described in JP-A-7-60110 (Patent Document 1).
[0006]
[Non-Patent Document 1]
Takagi, M., J. Phys. Soc. Jpn., 9 (1954), 359.
[Non-Patent Document 2]
Buffat, DA, and Borel, JP, Phys. Rev., A13 (1976), 2289.
[Patent Document 1]
Japanese Patent Laid-Open No. 7-60110
[Problems to be solved by the invention]
Furthermore, not only the gold nanoparticles themselves but also nanostructures using the gold nanoparticles are expected to exhibit new chemical and physical properties. In addition, nanostructures using gold nanoparticles are considered to be applicable to nanodevices.
[0008]
Accordingly, the present invention provides a method for producing a gold cobweb-like structure, a gold cobweb-like structure, a method for producing composite metal nanoparticles comprising a plurality of metals containing gold, and a composite metal that can solve the above-described problems. The object is to provide nanoparticles.
[0009]
[Means for Solving the Problems]
That is, a desirable embodiment of the present invention applies energy to gold nanoparticles in an aqueous solution containing a predetermined concentration of a surfactant or in water containing no surfactant.
[0010]
According to this, a gold cobweb-like structure can be obtained.
[0011]
The surfactant is an anionic surfactant. The surfactant is an alkali metal salt of an alkyl sulfate ester having 10 to 20 carbon atoms.
[0012]
Further, the application of energy is irradiation with a pulse laser beam having a predetermined number of shots.
[0013]
As the number of shots of pulsed laser light increases, a network of gold cobwebs grows.
[0014]
In addition, a desirable aspect of the present invention relates to a gold cobweb-like structure manufactured by the manufacturing method described above.
[0015]
Another desirable embodiment of the present invention applies energy to a plurality of metal nanoparticles including gold nanoparticles in an aqueous solution containing a predetermined concentration of a surfactant or in water not containing a surfactant.
[0016]
According to this, composite metal nanoparticles composed of a plurality of metals including gold can be obtained.
[0017]
The surfactant is an anionic surfactant. The surfactant is an alkali metal salt of an alkyl sulfate ester having 10 to 20 carbon atoms.
[0018]
Further, the application of energy is irradiation with a pulse laser beam having a predetermined number of shots.
[0019]
The other metal nanoparticles of the gold nanoparticles are platinum nanoparticles, and the mixing ratio of the gold nanoparticles and the platinum nanoparticles is greater than 70%.
[0020]
According to this, a cobweb-like structure in which gold nanoparticles and platinum nanoparticles are connected by gold nanowires can be obtained.
[0021]
Moreover, the other metal nanoparticles of the gold nanoparticles are platinum nanoparticles, and the mixing ratio of the gold nanoparticles and the platinum nanoparticles is less than 10%.
[0022]
According to this, a composite metal spherical colloid of platinum and gold is obtained.
[0023]
The other metal nanoparticles of the gold nanoparticles are platinum nanoparticles, and the mixing ratio of the gold nanoparticles and the platinum nanoparticles is 10% or more and 70% or less.
[0024]
According to this, a cobweb-like structure in which platinum nanoparticles are connected by gold nanowires can be obtained.
[0025]
Moreover, the desirable aspect of this invention is related with the composite metal nanoparticle manufactured by the above manufacturing methods.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described through embodiments of the invention.
[0027]
[Gold Cobweb Structure and Manufacturing Method]
FIG. 1 is a diagram illustrating a method for manufacturing a gold cobweb-like structure according to an embodiment. As the laser light source 10, for example, a neodymium yag laser that outputs laser light of 532 nm is used. As this laser beam, a pulsed laser beam having an energy density of about 5 J / pulse cm ² is used. Other laser beams may be used as long as sufficient energy can be irradiated.
[0028]
The laser light from the laser light source 10 is condensed by the condenser lens 12. The focal length of the condenser lens is determined by the position of the irradiation object. Below the condenser lens 12, a container 14 having at least a transparent or open upper part is disposed. In the container 14, an aqueous solution 16 containing gold nanoparticles and a surfactant is accommodated. As the surfactant, sodium lauryl sulfate is an anionic surfactant _{(SDS: C 12 H 25 OSO} 3 - Na +) is preferred, the energy density is the energy density of the laser to be irradiated is approximately 5 J / pulse cm ^In the case of ² , a concentration of 10 ⁻⁶ M or less is suitable. The surfactant is used for the purpose of reducing the stability and size of the nanoparticles in water. On the other hand, it is desirable that the surfactant be used as little as possible because it works in the direction of inhibiting the nanoparticles from becoming spider webs.
[0029]
The laser beam described above is condensed on the surface of the aqueous solution 16 by the condenser lens 12. The spot size of the laser beam is preferably 0.023 cm ² . When the surface of the aqueous solution 16 is irradiated with laser light, the plasmon band of the gold nanoparticle is excited at the irradiated point, and the gold nanoparticle is heated. With a single laser pulse, one gold nanoparticle continuously absorbs 1000 or more photons. For this reason, the temperature of the gold nanoparticles becomes higher than the melting point, and the gold nanoparticles start to fragment. After a single laser pulse irradiation, the heat of the gold nanoparticles diffuses into the aqueous solution 16, and the temperature of the gold nanoparticles returns to room temperature until the next laser pulse irradiation. Thus, every time the laser pulse is irradiated, the gold nanoparticles are heated and cooled.
[0030]
Microfragments such as gold clusters generated by laser irradiation diffuse into the aqueous solution 16. Gold nanoparticles present in the aqueous solution 16 grow by binding to these microfragments. Thereby, a gold cobweb-like structure in which the gold nanoparticles and the gold nanowires are connected to each other is generated in the aqueous solution 16. Typical examples of the diameters of gold nanoparticles and gold nanowires are about 10 to 100 nm and 10 nm, respectively.
[0031]
In the above example, a pulse laser is used as the energy source. However, the pulse may not be a pulse as long as gold nanoparticles can be melted, and the wavelength is not limited. Furthermore, as long as sufficient energy can be irradiated, an electric pulse (discharge), a microwave, or the like can be used without being limited to the laser.
[0032]
Moreover, in the above-mentioned example, although the aqueous solution of sodium laurate was used, it is not limited to this. That is, as the surfactant, a surfactant similar to sodium laurate and having a different hydrocarbon chain can be used. In addition, other surfactants may be used. Furthermore, alcohol, hydrocarbon, oil, etc. may be used in place of water. Furthermore, when the surfactant is different, the appropriate concentration range of the surfactant is naturally different.
[0033]
The gold cobweb structure thus obtained can be suitably applied as a nanodevice such as a molecular device or a nanofunctional device.
[0034]
Next, a specific experimental method will be described.
[0035]
(Preparation of gold nanoparticles)
A gold metal plate (purity:> 99.99%) was immersed and placed on the bottom of a glass container containing 10 ml of water. This gold metal plate was irradiated with a pulse laser having a wavelength of 1064 nm. The pulse frequency of the pulse laser was 10 Hz. When the laser power was 60 mJ / pulse, the speed at which gold was injected into the water as nanoparticles was 1 nmol / shot (1 nmol per laser shot).
[0036]
The produced gold nanoparticles were observed with an electron microscope (TEM: transmission electron microscope, magnification 50000 times). Within one field of view, more than 500 gold nanoparticles were seen. The diameter of these gold nanoparticles was measured. As a result, the average diameter of the gold nanoparticles was 20.7 nm, and the standard deviation was 13.1 nm.
[0037]
(Generation of a gold spider web structure)
As described above, gold nanoparticles prepared in water without surfactant were added to an aqueous solution of sodium lauryl sulfate (SDS) (concentration 10 ⁻⁶ M). An SDS solution containing gold nanoparticles was placed in an optical cell made of quartz and irradiated with a pulse laser with a wavelength of 532 nm (energy density 5 J / pulse cm ² ) for 20 minutes. The pulse frequency of the pulse laser was 10 Hz. A power meter (Scientech AC2501) was used to monitor the laser power. In order to make the spatial distribution of the gold nanoparticles in the SDS solution uniform, the SDS solution was stirred with a magnetic stirrer.
[0038]
FIG. 2 shows an electron microscope (TEM) photograph of a product obtained by irradiating gold nanoparticles in a 10 ⁻⁶ M SDS solution with a pulse laser (wavelength 532 nm, energy density 5 J / pulse cm ² ) for 20 minutes. Show. As shown in FIG. 2, a gold cobweb-like structure in which gold nanoparticles and gold nanowires were connected to each other was generated in the SDS solution. Typical examples of the diameters of gold nanoparticles and gold nanowires were about 10 to 100 nm and 10 nm, respectively.
[0039]
(Ultraviolet-visible absorption spectrum of gold cobweb structure)
FIG. 3 shows an ultraviolet-visible absorption spectrum of a gold cobweb structure. In FIG. 3, a dotted line shows the ultraviolet-visible absorption spectrum of the gold nanoparticle before irradiation with a pulsed laser having a wavelength of 532 nm. After the pulse laser irradiation, as shown in FIG. 3, a peak at 520 nm and a characteristic tail extending in the infrared wavelength region were observed. Comparing the UV-visible absorption spectra of gold nanoparticles before and after pulsed laser irradiation, the absorbance in the tail region increased significantly after pulsed laser irradiation, whereas the absorbance near the plasmon band formed a cobweb-like structure. It can be seen that the number decreases. Since a peak at a wavelength of 532 nm is observed in isolated spherical gold nanoparticles, the peak at a wavelength of 532 nm is assumed to be caused by light absorption by the spherical portion of the gold cobweb structure. On the other hand, the characteristic tail extending to the infrared wavelength region is an absorption that does not appear until a gold cobweb-like structure is formed, and is derived from an elongated shape.
[0040]
(Dependence of absorbance of gold cobweb structure on SDS concentration)
FIG. 4 is a graph showing the absorbance at 800 nm after irradiation with a pulse laser (wavelength 532 nm, energy density 4.3 J / pulse cm ² ) as a function of SDS concentration. When the absorbance (vertical axis) is around 0.2, it indicates that a spider web-like structure is generated. From the graph of FIG. 4, it can be seen that under the laser irradiation conditions, the gold cobweb structure is formed when the SDS concentration is less than 4 × 10 ⁻⁵ M. In the concentration region where the SDS concentration exceeds 5 × 10 ⁻⁵ M, the cobweb-like structure was not formed, and smaller gold nanoparticles were formed.
[0041]
(Laser shot number dependence of gold spider web structure)
FIG. 5 shows UV-visible as a function of the number of shots of the laser, in which a gold cobweb-like structure is gradually formed from gold nanoparticles by irradiation with a pulsed laser (wavelength 532 nm, energy density 1 J / pulse cm ² ). The absorption spectrum is shown. FIG. 5 shows that the characteristic tail extending to the infrared wavelength region gradually increases as the number of laser shots increases. It can also be seen that when the number of laser shots exceeds 4800, a small peak appears in the vicinity of 700 nm. This peak shifts to the longer wavelength side as the number of laser shots increases.
[0042]
FIG. 6 shows electron microscope (TEM) photographs of the gold nanoparticles and the gold web-like structure corresponding to FIGS. It can be seen that several gold nanoparticles are bonded by laser irradiation at 2400 shots. Bond generation is also shown in the spectral characteristics of the plasmon band. Gold nanoparticles solidify each other when laser irradiation is repeated, and finally form a network.
[0043]
(Dependence of gold cobweb structure on SDS concentration and laser intensity)
FIG. 7 shows the dependence of the gold spider web structure on SDS concentration and laser intensity. Specifically, FIG. 7 maps the absorbance at a wavelength of 800 nm as a function of the SDS concentration (horizontal axis) and the laser density (vertical axis) of the irradiated laser. Absorbance at a wavelength of 800 nm is an index indicating the formation of a gold cobweb structure and a decrease in size. In the region where the laser density of the irradiating laser is lower and the SDS concentration is higher, small gold nanoparticles are generated. In contrast, a gold cobweb-like structure is formed in a region where the laser density of the laser to be irradiated is higher and the SDS concentration is lower. The number density of gold microfragments generated by laser irradiation of gold nanoparticles increases as the laser density increases. Therefore, more SDS molecules are needed to stabilize all gold microfragments.
[0044]
Note that the degree of stabilization of the fine gold fragments by the surfactant varies depending on the type of the surfactant. Therefore, the surfactant concentration dependency of the formation of a gold cobweb structure in a surfactant different from that of SDS differs from that of SDS even under the same laser irradiation conditions as in SDS.
[0045]
(Composite metal nanostructure consisting of multiple metals including gold and its manufacturing method)
Next, a composite metal nanostructure composed of a plurality of metals including gold and a method for producing the same will be described. In the present embodiment, platinum is suitably used as the metal other than gold. The laser device used for manufacturing the composite metal nanostructure is the same as that shown in FIG. The laser irradiation conditions and the like are the same as in the case of manufacturing a gold cobweb structure. In the present embodiment, the container 14 contains an aqueous solution 16 containing gold nanoparticles and a surfactant. Similarly, as the surfactant, sodium lauryl sulfate (SDS) is preferably used.
[0046]
When the surface of the aqueous solution 16 is irradiated with laser light, the gold nanoparticles are fragmented, and microfragments such as gold clusters are diffused into the aqueous solution 16. Platinum nanoparticles present in the aqueous solution 16 grow by binding to these microfragments. Thereby, in the aqueous solution 16, a composite metal structure in which platinum nanoparticles and gold nanowires are connected to each other is generated.
[0047]
Note that the platinum nanoparticles may be fragmented depending on the energy density of the laser beam. Depending on the energy density of the laser beam, gold and platinum may be alloyed.
[0048]
Moreover, the composite metal structure to be produced differs depending on the mixing ratio of gold and platinum (the atomic ratio, [gold] / ([gold] + [platinum])). When the mixing ratio is 70% or more, a cobweb-like composite metal structure in which gold nanoparticles and platinum nanoparticles and gold nanowires are connected to each other is generated. When the mixing ratio is 10% or less, a composite metal spherical colloid of platinum and gold is formed.
[0049]
It is suggested from the absorption spectrum described later that the composite metal structure obtained in this way is physically connected (has electrical conductivity).
[0050]
The composite metal structure described above can be suitably applied as a nanodevice such as a molecular device or a nanofunctional device.
[0051]
Next, a specific experimental method will be described.
[0052]
(Preparation of gold nanoparticles and platinum nanoparticles)
A gold metal plate (purity:> 99.99%) was immersed and placed on the bottom of a glass container containing 10 ml of water. This gold metal plate was irradiated with a pulse laser having a wavelength of 1064 nm. The pulse frequency of the pulse laser was 10 Hz.
[0053]
Similarly, a platinum metal plate (purity:> 99.99%) was immersed and placed on the bottom of a glass container containing 10 ml of water. The platinum metal plate was irradiated with a pulse laser having a wavelength of 1064 nm. The pulse frequency of the pulse laser was 10 Hz.
[0054]
FIG. 8 is a diagram showing an ultraviolet-visible absorption spectrum of the generated gold nanoparticles (broken line) and platinum nanoparticles (solid line). In the spectrum of gold nanoparticles, the peak at 532 nm is derived from isolated gold nanoparticles. The platinum nanoparticles do not have a characteristic peak.
[0055]
(Generation of gold-platinum nanostructures)
The aqueous solution containing the generated gold nanoparticles and the aqueous solution containing platinum nanoparticles were mixed at a mixing ratio ([gold] / ([gold] + [platinum])) 0.36.
[0056]
An aqueous solution containing gold nanoparticles and platinum nanoparticles prepared in water that does not contain a surfactant is placed in an optical cell made of quartz, and a pulse laser with a wavelength of 532 nm (energy density 2.2 J / pulse cm ² ) is applied for 10 seconds. Irradiation (1000 shots). The pulse frequency of the pulse laser was 10 Hz. A power meter (Scientech AC2501) was used to monitor the laser power. In order to make the spatial distribution of the gold nanoparticles in the SDS solution uniform, the SDS solution was stirred with a magnetic stirrer.
[0057]
FIG. 9 shows ultraviolet and visible products obtained by irradiating gold nanoparticles and platinum nanoparticles with 1000 shots of pulsed laser (wavelength of 532 nm, energy density of 2.2 J / pulse cm ² ) in water containing no surfactant. An absorption spectrum is shown. The broken line in FIG. 9 shows the absorption spectrum of the solution before laser irradiation, and the solid line shows the absorption spectrum of the solution after laser irradiation. Thus, it can be seen that the 532 nm peak characteristic of isolated gold nanoparticles is almost invisible by laser irradiation.
[0058]
FIG. 10 shows an electron microscope (TEM) photograph of composite metal nanoparticles composed of gold and platinum. As shown in FIG. 10, cobweb-like composite metal nanoparticles in which platinum nanoparticles (spherical portions) and gold nanowires were connected to each other were generated in water. Typical examples of the diameters of platinum nanoparticles and gold nanowires were about 20 to 30 nm and about 10 nm, respectively.
[0059]
(Dependence on mixing ratio of gold-platinum nanostructure)
It was found that the morphology of the gold-platinum nanostructure varies depending on the mixing ratio of gold and platinum.
[0060]
In FIG. 11, 1000 shots of pulsed laser (wavelength 532 nm, energy density 2.2 J / pulse cm ² ) were irradiated in water with different mixing ratios of gold and platinum ([gold] / ([gold] + [platinum])). The later UV-visible absorption spectrum is shown.
[0061]
As shown in FIG. 11, when the mixing ratio is greater than 70%, a shoulder is observed near 532 nm, suggesting that gold nanoparticles remain. That is, when the mixing ratio is greater than 70%, it is presumed that a cobweb-like structure in which gold nanoparticles and platinum nanoparticles are connected by gold nanowires is formed. Further, when the mixing ratio is 10% or more and 70% or less, it is assumed that the particulate gold disappears, and a cobweb-like structure in which platinum particles are connected by a gold wire is formed. When the mixing ratio is less than 10%, a spider web-like structure is not formed, and a composite metal spherical colloid of platinum and gold is formed. The formation of spherical colloid is also indicated by the feature that the absorption spectrum of the product does not tail on the long wavelength side. Although the detailed structure of gold and platinum of the composite metal spherical colloid is unknown, it is assumed that it takes a core-shell or random structure.
[0062]
In the above embodiment, the composite metal nanoparticles composed of gold and platinum and the manufacturing method thereof have been described. However, the metal combined with gold is not limited to platinum, and silver, palladium, rhodium, ruthenium, iron, chromium, nickel, and the like. Transition metals and their oxides can also be used. It can also be used for composite metal nanoparticles made of metals other than gold. In this experiment, gold is melted by exciting gold and gold and another metal are bonded, but platinum can be excited by exciting the laser wavelength, and another metal can be excited.
[0063]
【The invention's effect】
As is apparent from the above description, according to the present invention, a gold cobweb-like structure is formed by applying energy to gold nanoparticles in an aqueous solution containing a surfactant or in water containing no surfactant. Can be obtained.
[0064]
Further, according to the present invention, a plurality of metals containing gold by applying energy to a plurality of metal nanoparticles containing gold in an aqueous solution containing a surfactant or in water containing no surfactant. Cobweb-like composite metal nanoparticles or composite metal spherical colloids can be obtained.
[Brief description of the drawings]
FIG. 1 is a view showing a method for producing a gold web-like structure according to an embodiment.
FIG. 2 shows an electron microscope (TEM) photograph of a product obtained by irradiating gold nanoparticles in a 10 ⁻⁶ M SDS solution with a pulse laser (wavelength 532 nm, energy density 5 J / pulse cm ² ) for 20 minutes. FIG.
FIG. 3 is a diagram showing an ultraviolet-visible absorption spectrum of a gold cobweb-like structure.
FIG. 4 is a graph showing absorbance at 800 nm after irradiation with a pulse laser (wavelength: 532 nm, energy density: 4.3 J / pulse cm ² ) as a function of SDS concentration.
FIG. 5 shows UV-visible as a function of the number of shots of a laser, in which a gold cobweb-like structure is gradually formed from gold nanoparticles by irradiation with a pulsed laser (wavelength 532 nm, energy density 1 J / pulse cm ² ). It is the figure shown by the absorption spectrum.
6 is a view showing an electron microscope (TEM) photograph of the gold nanoparticles and the gold web-like structure corresponding to FIGS. 5 (a) to 5 (c). FIG.
FIG. 7 is a diagram showing the dependency of the formation of a gold cobweb structure on the SDS concentration and laser intensity.
FIG. 8 is a diagram showing ultraviolet-visible absorption spectra of generated gold nanoparticles (broken line) and platinum nanoparticles (solid line).
FIG. 9 shows UV-visible products obtained by irradiating gold nanoparticles and platinum nanoparticles in water containing no surfactant for 20 minutes with a pulse laser (wavelength of 532 nm, energy density of 2.2 J / pulse cm ² ). It is a figure which shows an absorption spectrum.
FIG. 10 is an electron microscope (TEM) photograph of composite metal nanoparticles made of gold and platinum.
FIG. 11 is a diagram showing an ultraviolet-visible absorption spectrum after laser irradiation in water with different mixing ratios of gold and platinum ([gold] / ([gold] + [platinum])).
[Explanation of symbols]
10 laser light source, 12 condenser lens, 14 container, 16 aqueous solution.

Claims (11)

In an aqueous solution containing a predetermined concentration of the surfactant or water without surfactant, and gold nanoparticles by the application of energy by the pulse laser beam irradiation of a predetermined number of shots, producing a web-like structure of the gold A method for producing a gold cobweb-like structure. The method of claim 1, wherein
The method for producing a gold cobweb-like structure, wherein the surfactant is an anionic surfactant. The method according to claim 1 or 2, wherein
The method for producing a gold cobweb-like structure, wherein the surfactant is an alkali metal salt of an alkyl sulfate ester having 10 to 20 carbon atoms.   A gold web-like structure manufactured by the manufacturing method according to claim 1. In an aqueous solution containing a predetermined concentration of the surfactant or water without surfactant, and a plurality of metal nanoparticles comprising gold nanoparticles, by the application of energy by the pulse laser beam irradiation of a predetermined number of shots, the gold A method for producing composite metal nanoparticles, comprising producing composite metal nanoparticles. The method of claim 5, wherein
The method for producing composite metal nanoparticles, wherein the surfactant is an anionic surfactant. The method according to claim 5 or 6, wherein
The method for producing composite metal nanoparticles, wherein the surfactant is an alkali metal salt of an alkyl sulfate ester having 10 to 20 carbon atoms. The method according to any one of claims 5 to 7,
The other metal nanoparticles of the gold nanoparticles are platinum nanoparticles,
A method for producing composite metal nanoparticles, wherein a mixing ratio of the gold nanoparticles and the platinum nanoparticles is greater than 70%. The method according to any one of claims 5 to 7,
The other metal nanoparticles of the gold nanoparticles are platinum nanoparticles,
A method for producing composite metal nanoparticles, wherein a mixing ratio of the gold nanoparticles and the platinum nanoparticles is less than 10%. The method according to any one of claims 5 to 7,
The other metal nanoparticles of the gold nanoparticles are platinum nanoparticles,
A method for producing composite metal nanoparticles, wherein a mixing ratio of the gold nanoparticles and the platinum nanoparticles is 10% or more and 70% or less.   The composite metal nanoparticle manufactured by the manufacturing method of any one of Claims 5 thru | or 10.

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