Patent Application
20190165190
The present invention relates to nanoparticle assemblies and a method for producing nanoparticle assemblies. The present invention claims the priority of JP 2016-157933 A filed on Aug. 10, 2016 the contents of which are hereby incorporated by reference for designated countries that allow incorporation by reference of the literature.
As an example of nanoparticle assemblies used for solar cells or the like, JP 2011-213505 A discloses “a titanium oxide nanoparticle assembly which includes titanium oxide nanoparticles (A) having an average primary particle size of 20 nm or less, and which has an average diameter of 30 to 500 nm.” Nanoparticles are used not only for solar cells but also for photocatalysts, filtration filters, and the like. However, a nanoparticle production method in the related art limits the size of nanoparticle assemblies to be produced.
A first aspect of the present invention is a nanoparticle assembly which includes a nanoparticle having an average primary particle size of 60 nm or less, and which has a diameter of more than 500 nm and 5 μm or less.
A second aspect of the present invention is a method for producing a nanoparticle assembly according to the first aspect, the method involving: mist generation in which a solution containing a nanoparticle is prepared and mist of the solution is generated; plasma generation in which a plasma is generated between a first electrode and a second electrode; and nanoparticle assembly production in which the mist is supplied between the first electrode and the second electrode and in which a nanoparticle assembly is generated. In the plasma generation, the plasma has a ratio of emission intensities (I391/I357) of 0.072 or more and less than 0.08, where I391 is an emission intensity at a wavelength of 391 nm and I357 is an emission intensity at a wavelength of 357 nm.
Hereinafter, an exemplary embodiment of the present invention will be described.
In this embodiment, described is a method for producing a nanoparticle assembly with a nanoparticle assembly producing apparatus 11 shown in
A nanoparticle assembly produced in this embodiment is an assembly including assembled nanoparticles. In other words, the nanoparticle assembly is a secondary particle which is formed of nanoparticles which are primary particles are assembled. In this embodiment, examples of the assembly include an aggregate and a polycrystal.
The nanoparticle assembly includes nanoparticles which are the primary particles having an average particle size of 60 nm or less, and the nanoparticle assembly has a diameter of more than 500 nm and 5 μm or less. The average particle size herein represents a mean number diameter of particles obtained by a dynamic light-scattering particle size analyzer. The diameter of the nanoparticle assembly herein represents a value obtained from a mean value of the long axis and the short axis of the nanoparticle assembly in an image of the nanoparticle assembly observed by SEM.
It is desirable that the nanoparticle assembly has a diameter of more than 800 nm and 5 μm or less. More desirably, the nanoparticle assembly has a diameter of more than 1 μm and 5 μm or less. The nanoparticle assembly is preferably used for, for example, a photocatalyst, a solar cell, and a diffuser plate.
In order to obtain a preferable nanoparticle assembly, it is desirable that the nanoparticles have an average primary particle size of more than 10 nm and 50 nm or less. More desirably, the nanoparticles have an average primary particle size of more than 20 nm and 40 nm or less.
Examples of the nanoparticles include mixed oxides, mixed fluorides, and mixed nitrides of one or more kinds of indium, zinc, tin, titanium, tantalum, and gallium, specifically, MgO, Al2O3, SiO2, TiO2, VO2, Mn2O3, Fe2O3, NiO, CuO, ZnO, Ga2O3, Nb2O3, AgO, SnO2, Sb2O3, MgF2, AlN, Si3N4, TiN, FeN, BN, InN, and SbN. Alternatively, instead of oxides, the nanoparticles may be mixed metals of one or more kinds of indium, zinc, tin, titanium, tantalum, and gallium. The nanoparticles may also be organic compounds containing polystyrene and the like.
The plasma generation unit 110 includes an electrode 111A, an electrode 111B, a mist route 112, and a substrate holder 113. The electrode 111A is a high-voltage electrode, and the electrode 111B is a ground electrode. The electrode 111A and the electrode 111B are electrodes each including a metallic conductive wire covered with a dielectric, as described later in detail. Application of a voltage generates a plasma between the electrode 111A and the electrode 111B. The mist route 112 guides mist generated in the mist generation unit 120 between the electrodes. Being influenced by the plasma generated between the electrodes, the mist leads to formation of an assembly.
The substrate holder 113 places a substrate FS above the plasma generation unit 110. A commonly used material is employable as the substrate FS. Examples of the material include glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyether ether ketone, polyphenylenesulfide, polyarylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), and cellulose acetate propionate (CAP).
The mist generation unit 120 includes a mist generation tank 121, an ultrasonic transducer 122, and a gas inlet pipe 123. The mist generation tank 121 accumulates a precursor LQ. The precursor LQ is produced by dispersing the nanoparticles which are the primary particles in a dispersion medium. In this embodiment, metal oxide particulates are used as particulates. The dispersion medium is not limited as long as particulates are dispersible therein, and may be water, alcohol such as isopropyl alcohol (IPA) and ethanol, and a mixture thereof.
The ultrasonic transducer 122 generates ultrasonic waves and mists the precursor LQ inside the tank. The gas inlet pipe 123 supplies gas to the mist generation tank 121. The gas introduced into the gas inlet pipe 123 is, for example, Ar, but is not limited thereto.
A process flow according to this embodiment will now be described. First, in the mist generation tank 121, the ultrasonic transducer 122 mists the accumulated precursor LQ. Next, mist including the nanoparticles is supplied to the mist route 112 by the gas supplied from the gas inlet pipe 123. Next, the mist supplied to the mist route 112 passes between the electrode 111A and the electrode 111B.
At this time, the nanoparticles included in the mist are excited by the plasma generated by application of a voltage to the electrode 111A and the electrode 111B, whereby forming an assembly. The nanoparticle assembly formed herein adheres to a surface of the substrate FS. Note that the assembly formed herein has a substantially spherical shape. When producing an object such as a filter with the nanoparticle assembly, since the nanoparticle assembly has a substantially spherical shape, it is possible to produce an appropriate object.
In this embodiment, the mist that has passed through the mist route 112 having a substantially ring shape passes between the electrode 111A and the electrode 111B, causing the nanoparticles to form an assembly.
The electrode 111A includes a wire electrode EP and a dielectric Cp. The electrode 111B includes an electrode EG and a dielectric Cg. The electrode EP and the electrode EG are not limited in materials as long as they are a conductor. Examples of the materials include tungsten and titanium.
The electrode EP and the electrode EG are not limited to wires and may be flat plates. However, in a case where flat plates are used as electrodes, it is desirable that surfaces including opposing edges are parallel to each other. Each electrode may be formed of a flat plate having a sharp edge like a knife. However, in that case, an electric field is concentrated at the edge, which may cause arcing. It is desirable that each electrode has a wire shape rather than a flat plate shape because a small surface area of the electrode improves efficiency in plasma generation.
The electrode EP and the electrode EG are hereinafter described as being straight, but may be bent.
A dielectric is used as the dielectric Cp and the dielectric Cg. Examples of the dielectric Cp and the dielectric Cg include quartz and ceramics (insulating material such as silicon nitride, zirconia, alumina, silicon carbide, aluminum nitride, and magnesium oxide).
In this embodiment, a plasma is generated by dielectric barrier discharge. Therefore, it is necessary to provide a dielectric between the electrode EP and the electrode EG. A relative positional relationship between a metallic conductive wire and a dielectric is not limited to the example shown in
The mist generated in the mist generation tank 121 is guided to the mist route 112 and reaches the electrode 111A and the electrode 111B. The mist is excited by the plasma generated between the electrodes, leading to formation of an assembly. Although the nanoparticle assembly producing apparatus 11 shown in
The nanoparticle assembly producing apparatus 11 requires a shorter forming time than a wet-type method in the related art for forming an assembly. In other words, the nanoparticle assembly producing apparatus 11 efficiently forms a highly versatile nanoparticle assembly.
An emission spectrum of N2 is obtained in an atmospheric-pressure plasma. In the emission spectrum, there are emission attributed to a first negative band of N2+ at a wavelength of 391 nm and emission attributed to a second positive band of N2* at a wavelength of 357 nm. It is known that a ratio of an emission intensity attributed to the first negative band and an emission intensity attributed to the second positive band is correlated with an electron temperature of a plasma. Using this ratio enables quantification of plasma states. In this embodiment, an emission intensity of an atmospheric-pressure plasma at a wavelength of 391 nm (I391) and an emission intensity at a wavelength of 357 nm (I357) are measured by fiber spectroscopy. Values representing a ratio (I391/I357) of these emission intensities are taken along the ordinate of
Using a power source having a pulse width of 500 ns and a voltage rise time of 200 ns or less, a more stable plasma is generated. In regard to a power source, it is desirable to use one that stably maintains discharge and applies a high voltage. Specifically, it is desirable that a voltage to be applied to the electrodes is 16 kV or more and less than 20 kV. Furthermore, a frequency of the voltage to be applied to the electrodes is desirably 6 kHz or more and less than 11 kHz.
<First Modification of Nanoparticle Assembly Producing Apparatus>
The plasma generation unit 210 includes an electrode 211A and an electrode 211B. The mist generation unit 220 includes a mist generation tank 221, an ultrasonic transducer 222, and a gas inlet pipe 223. The electrode 211A, the electrode 211B, the mist generation tank 221, the ultrasonic transducer 222, and the gas inlet pipe 223 are similar to the electrode 111A, the electrode 111B, the mist generation tank 121, the ultrasonic transducer 122, and the gas inlet pipe 123 in the above-mentioned embodiment.
The mist generation unit 220 and the mist trap 230 are connected by a mist route 212, and mist generated in the mist generation unit 220 is transmitted to the mist trap 230. In the mist trap 230, unnecessary mist is liquefied and accumulated. The mist trap 230 and the plasma generation unit 210 are connected by the mist route 212, and mist that is not liquefied is guided to the plasma generation unit 210.
Vaporization of moisture in nanoparticles that have passed between the electrodes in the plasma generation unit 210 leads to formation of a nanoparticle assembly which is a secondary particle. As shown in
<Second Modification of Nanoparticle Assembly Producing Apparatus>
The pair of electrodes 111A (111B) includes a wire electrode EP extending in the Y direction beyond the length La and a wire electrode EG extending in the Y direction beyond the length La. The electrodes EP and EG are held in cylindrical quartz tubes functioning as a dielectric Cp and a dielectric Cg, respectively, and are parallel to each other at a predetermined interval in the Xt direction. The quartz tubes are fixed to the leading end of the plasma generation unit 310, being positioned on both sides of the slot-shaped opening SN. It is desirable that the quartz tubes do not contain a metal component inside. Furthermore, the dielectrics Cp and Cg may be ceramic tubes having a high dielectric strength voltage.
The present invention will be explained in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited to the following Examples.
A nanoparticle assembly was produced with the nanoparticle assembly producing apparatus 21 described with reference to
A voltage was applied to the ultrasonic transducer 222 (manufactured by Honda Electronics Co., Ltd.), and the ultrasonic transducer 222 was vibrated at 2.4 MHz to generate mist from the precursor LQ. The mist generated herein was transmitted to the plasma generation unit 210, using Ar gas.
Ti wires were used for the electrode EP and the electrode EG which were covered with the dielectric Cp and the dielectric Cg including SiO2. An interval between the dielectric Cp and the dielectric Cg was 2 mm. In the plasma generation unit 210, a voltage in 19 kV was applied between the electrodes, and an atmospheric-pressure plasma was generated at a frequency of 10 kHz.
Using the nanoparticle assembly producing apparatus 21 described with reference to
Using the nanoparticle assembly producing apparatus 21 described with reference to
Using the nanoparticle assembly producing apparatus 21 described with reference to
The result showed that an ITO film was formed on the substrate, and a nanoparticle assembly was not observed. In regard to the production conditions of Comparative Example 1, as shown in
Using the nanoparticle assembly producing apparatus 21 described with reference to
The result showed that an ITO film was formed on the substrate, and a nanoparticle assembly was not observed. In regard to the production conditions of Comparative Example 2, as shown in
Using the nanoparticle assembly producing apparatus 21 described with reference to
The result showed that an ITO film was formed on the substrate, and a nanoparticle assembly was not observed. In regard to the production conditions of Comparative Example 3, as shown in
Using the nanoparticle assembly producing apparatus 21 described with reference to
The result showed that no matter which frequencies of 8 kHz, 6 kHz, 4 kHz or 2 kHz was used when the voltage was applied between the electrodes, an ITO film was formed on the substrate, and a nanoparticle assembly was not observed.
Considering the above Examples 1 to 3 and Comparative Example, it is desirable that a voltage to be applied to the plasma generation unit 210 is 16 kV or more and less than 20 kV. Applying an appropriate voltage yields a preferable nanoparticle assembly. The results of Examples 1 to 3 show that an average diameter of the nanoparticle assemblies tends to increase with an increase in frequency of a voltage applied to the electrodes.
A nanoparticle assembly was produced using the nanoparticle assembly producing apparatus 21 described with reference to
In the plasma generation unit 210, a voltage in 19 kV was applied between the electrodes, and an atmospheric-pressure plasma was generated at a frequency of 10 kHz. Other production conditions are similar to those in Example 1.
In Example 4, substantially spherical nanoparticle assemblies having different sizes was obtained. Examples 1 and 4 show that it is also possible to yield a preferable assembly from nanoparticles other than ITO.
An aqueous dispersion containing GZO particulates was prepared. Using the nanoparticle assembly producing apparatus 21 described with reference to
An aqueous dispersion containing GZO particulates was prepared. Using the nanoparticle assembly producing apparatus 21 described with reference to
The results of Examples 4 to 6 show that, even when GZO particles are used for nanoparticles, an average diameter of the nanoparticle assemblies tends to increase with an increase in frequency of a voltage applied to the electrodes, as in the case where ITO particulates are used for nanoparticles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-157933 | Aug 2016 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2017/026295 | Jul 2017 | US |
| Child | 16263921 | US |
