JP7133183B2 - VO2-supporting hollow particles having thermochromic properties and method for producing the same - Google Patents

Description

The present invention relates to hollow particles and methods for their production.

The inventors have established a method for producing nano-sized hollow particles. Nano-sized hollow particles have air inside, and thus have low thermal conductivity. Moreover, since they are minute, they have high transparency. Therefore, a film made of nano-sized hollow particles is transparent and highly heat-insulating, and when applied to a windowpane, it can insulate without impairing visibility.

US Pat. No. 6,200,000 describes hollow particle films with VO ₂ particles having thermochromic properties. The thermochromic property is that the transmittance of light changes with temperature, and the transmittance decreases when the temperature is higher than the transition temperature.

On the other hand, since the VO2 particles are black, the transmittance of hollow particle films with VO2 particles is reduced. Therefore, the smaller the particle size of the VO2 particles, the better. If it is 10 nm or less, a hollow particle film having VO2 particles with excellent visible light transmittance can be obtained.

However, in the conventional method of pulverizing solidified VO ₂ into fine powder and supporting it on hollow particles, it was difficult to make the particle size of VO ₂ particles 10 nm or less.

WO2016/017611

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems of conventional production methods, and to provide hollow particles supporting _VO2 particles having a particle size of 10 nm or less and a production method thereof.

Means for solving the above problems include the following inventions.
In Invention 1, a hollow particle template (7) and a dispersion (10) containing VO ions (9) are stirred to form core-shell particles (5) containing VO ions (9) in silica shells (6). , remove the template (7) by washing the core-shell particles (5) with water, retain water inside, further evaporate the water inside by heat treatment in an inert atmosphere, and form VO in the silica shell (6) A method for producing VO ₂ -supported hollow particles (1) having shells (3) supporting ₂ particles (8). Invention 2 is a method for producing VO ₂ -supported hollow particles (1) according to Invention 1, wherein the VO ₂ particles (8) are 10 nm or less. Invention 3 is a VO ₂ -supported hollow particle (1) supporting VO ₂ particles (8) having thermochromic properties, wherein the VO ₂ particles (8) have a size of 10 nm or less, and at a transition temperature or lower, transmission The VO ₂ -supporting hollow particles (1) are characterized in that the transmittance at a wavelength of 800 nm or more is reduced when the transmittance is 30% or more and 90% or less and the transition temperature or more. Invention 4 is the VO ₂ -supporting hollow particles (1) according to Invention 3, characterized in that the transition temperature is from 50°C to 70°C.
It should be noted that the symbols in parentheses in the above description and the scope of the claims indicate the correspondence relationship between the terms described in the scope of claims and specific objects described in the embodiments described later and serving as examples of the terms. be.

According to the means described above, the shell 3 of the VO ₂ -supported hollow particles 1 can be produced from the silica shell 6 and the VO ions 9 . Therefore, the VO2 _- supporting hollow particles 1 having the shell ₃ having the VO2 particles 8 of 10 nm or less can be produced, and a VO2-supporting hollow particle film excellent in visible light transmittance can be provided.

1 shows the synthesis procedure of VO2 _- loaded hollow particles. Schematic representation of the structure of VO2 _- loaded hollow particles in the synthesis procedure. Figure ₂ shows the XRD pattern of VO2-loaded hollow particles. SEM observations are shown. (a) VO2 _- supported hollow particles, ( _b ) VO2 crystals (conventional) Thermochromic properties (UV-vis, transition temperature 67° C.) of VO ₂ -loaded hollow particle films are shown. The effect of the smart window (summer) is shown schematically. Schematically shows the effect of smart windows (in winter). 1 shows the transmittance of a conventional hollow particle film.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

(Production method)
1 and 2 show the procedure for synthesizing the VO ₂ -supported hollow particles 1. FIG.
Step S101 mixes polyacrylic acid (PAA) and sodium hydroxide (NaOH) aqueous solution to make hollow particle template 7 . As an example, 0.09 g of PAA and 0.75 ml of 1M (mol/L) NaOH aqueous solution are mixed.
Step S102 mixes the V source as VO ions 9 and the base as catalyst to produce VO2 particles ₈ from the ions. V sources include V ₂ O ₅ , NH ₄ VO ₃ , NaVO ₃ , VOSO ₄ and the like. Bases include NH ₃ , NaOH, and the like. As an example, the V source was vanadium oxide sulfate (VOSO4) and the base was mixed using a 1 M NaOH aqueous solution. In step S103, a mixed liquid is created from steps S101 and S102 and dropped. A step S104 drops the mixed liquid of the step 103 into ethanol. FIG. 2(a) shows a hollow particle template. When a mixture (liquid) of PAA, NaOH, and a V source is dropped into ethanol, PAA aggregates 7, which are fine templates, are formed because the mixture is insoluble in ethanol. Accordingly, PAA aggregates 7, Na ions, VO ions 9, and SO ₄ ions are dispersed in ethanol (hereinafter referred to as dispersion liquid 10). This PAA aggregate 7 serves as a template for producing hollow particles.

In step S105, the dispersion liquid 10 is stirred using a magnetic stirrer, an ultrasonic homogenizer, a rotary homogenizer, a jet mill, or the like. The fine PAA aggregates 7 become spherical by stirring, and VO ions 9 are present in the surrounding ethanol. In step S106, TEOS (tetraethoxysilane) is dripped into the dispersion liquid 10 being stirred in order to form the silica shell 6 that serves as the shell of the hollow particles. TEOS adheres to the surface of PAA aggregates 7 to form a silica shell 6 . At this time, VO ions 9 are present at the interface between the PAA aggregates 7 and the silica shell 6 . In addition, the silica shell 6 increases its film thickness while taking in TEOS and VO ions 9 from the dispersion liquid 10 being stirred. This state is shown in FIG. AA aggregates 7 are formed on the inside, VO ions 9 on the outside, and a thin film of silica shell 6 on the outside. Furthermore, VO ions 9 adhere to the outside of the thin film of silica shell 6 . That is, silica shells 6 and VO ions 9 are formed in layers. Consequently, core-shell particles 5 having AA aggregates 7 inside and silica shells 6 containing VO ions 9 outside thereof are finally formed. As an example, 0.75 ml of TEOS was added dropwise over 20 hours, and a silica shell 6 containing VO ions 9 was formed by stirring. TEOS (tetraethoxysilane) may be MTES (methyltriethoxysilane), MTMS (methyltrimethoxysilane), dimethyltrimethoxysilane, dimethyltriethoxysilane, tetrachlorosilane, or water glass.

In step S107, the dispersion liquid 10 containing the core-shell particles 5 obtained in S106 is subjected to solid-liquid separation (solid: core-shell particles 5, liquid: ethanol, unreacted TEOS, etc.) by centrifugation. As an example, it was performed at 15,000 rpm for 10 minutes.
In step S108, after washing the core-shell particles 5 obtained in S107 with ethanol, distilled water is added to dissolve the PAA aggregates 7 (PAA, NaOH) inside, and solid-liquid separation is performed by centrifugation to obtain a V source. Hollow particles consisting of silica shells 6 containing VO ions 9 are obtained. This is a state in which distilled water is added to core-shell particles 5 to dissolve and remove internal PAA, Na, SO4 ions, and the like. The inside is filled with distilled water. As an example, two washes with added distilled water were performed.
In step S109, the hollow particles of silica shell 6 containing VO ions 9 with distilled water inside obtained in S108 are heat-treated to volatilize the distilled water inside to make them hollow. When the VO ions 9 are heat-treated, the VO ions 9 are oxidized to V2O5 via V2O3 and the like. Since what we want is VO2, it is necessary to suppress oxidation. Therefore, heat treatment must be performed in an oxygen-free inert atmosphere. An inert gas is used as the inert atmosphere. The inert gas includes nitrogen (N2), argon (Ar), and helium (He), and a vacuum pump or the like may be used to create a reduced pressure atmosphere. Alternatively, the treatment can be performed in a reducing atmosphere. Hydrogen (H2) is used as a reducing atmosphere gas. Considering the cost and safety, a reduced pressure atmosphere and nitrogen (N2) are the best. The VO ions 9 change into VO2 particles 8 when heat-treated in an inert atmosphere (see FIG. 3). As a result, VO ₂ -supported hollow particles 1 in which VO ₂ particles 8 were supported on silica shells 6 as shells 3 shown in FIG. 2(c) were obtained. As an example, drying was performed at 600° C. for 1 hour in a nitrogen atmosphere at 10° C./min.

(VO2 _- loaded hollow particles)
FIG. 3 shows the XRD pattern of VO ₂ -loaded hollow particles 1 . The master VO2 (PDF card number _82-0661 ) and the VO2 _- loaded hollow particles 1 obtained by the method shown in FIG. It was confirmed that

FIG. 4(a) shows SEM observation of the VO ₂ -loaded hollow particles 1. FIG. The VO ₂ -supported hollow particles 1 have a translucent shell 3 in which black VO ₂ particles 8 are supported on a transparent silica shell 6, and the outer diameter of the shell 3 is about 10 to 100 nm. The outer diameter of the VO ₂ particles 8 cannot be confirmed by SEM observation. Therefore, it is 1 nm or less. This is due to the generation of VO ₂ particles 8 from ions. On the other hand, it is also possible to grow the VO ₂ particles 8 to about 10 nm depending on the manufacturing conditions.

FIG. 4( _b ) shows a VO2 crystal 108 (conventional). These are solids larger than 1 μm. This is made into a fine powder and carried on the hollow particles. There is a limit to miniaturization, and it is extremely difficult to reduce the average particle size to 10 nm or less.

(smart window)
FIG. 8 shows the transmittance of a conventional hollow particle film 120 ₍ without VO2 particles) made by the inventors. It exhibits a high transmittance of about 85% at a wavelength of 300 nm or more.

FIG. 5 shows the VO ₂ thermochromic properties (UV-vis, transition temperature 67° C.). At room temperature (15-35° C.), the transmittance is about 35% regardless of wavelength. On the other hand, at 90° C., which is higher than the transition temperature, the transmittance was 35% at 400 to 800 nm, which is visible light, which is the same as at room temperature, but at 800 nm or more, the transmittance decreased by 10% to about 25%. Incidentally, the transition temperature of the VO ₂ particles 8 can be adjusted.

FIG. 6 shows a smart window (summer) in which the VO ₂ -loaded hollow particle film 20 is applied to the window 30 . The VO ₂ -supporting hollow particle film 20 is obtained by dispersing the VO ₂ -supporting hollow particles 1 in a transparent resin film and adhering them. As an example, the temperature of the outdoor 35 is 35° C., the temperature of the indoor 32 is 25° C., and the amount of solar radiation (500 Wh) is absorbed by the window glass. Intrusion heat due to heat conduction from the outdoor 35 to the indoor 33 is reduced by thermal insulation. In addition, the temperature of the windowpane 30 becomes 80° C. (which varies depending on the heat capacity of the windowpane), which is higher than the transition temperature. Therefore, the transmission of sunlight is blocked and becomes small. As described above, the heat load is reduced, and the electric power required for cooling can be reduced.

FIG. 7 shows a smart window (winter) in which the VO ₂ -loaded hollow particle film 20 is applied to the window 30 . The VO ₂ -supporting hollow particle film 20 is obtained by dispersing the VO ₂ -supporting hollow particles 1 in a transparent resin film and adhering them. As an example, the temperature of the outdoor 35 is 0° C., the temperature of the indoor 32 is 20° C., and the amount of solar radiation (500 Wh) is absorbed by the window glass. The heat released by heat conduction from the indoor 33 to the outdoor 35 is reduced by heat insulation. On the other hand, the temperature of the windowpane 30 becomes 45° C. below the transition temperature (varies depending on the heat capacity of the windowpane). Therefore, the transmission of sunlight is not blocked. As described above, the heat load is reduced by the sunlight, and the electric power required for heating can be reduced.

A smart window can be provided by a VO2 _- loaded hollow particle film 20 using VO2 _- loaded hollow particles 1 loaded with VO2 particles ₈ having thermochromic properties. The VO ₂ particles 8 have a size of 10 nm or less, and have a transmittance of 30% or more and 90% or less below the transition temperature, and can reduce the transmittance at a wavelength of 800 nm or above above the transition temperature. Also, the transition temperature is preferably in the range of 50° C. to 70° C. from the conditions of FIGS.

(Smart window effect)
We have invented VO2 _- supporting hollow particles 1 that have _both the heat-shielding function of the VO2 particles 8 with temperature responsiveness and the super heat insulation of the hollow particles. The VO ₂ -supporting hollow particles 1 can reduce the power consumption of air conditioning by 30% or more in summer and winter or at any time of day and night. A _CO2 reduction of about 40 million tons/year can be expected. In general, a light-shielding film in summer has an energy-saving effect of 30%, but it has a negative effect in winter. About 25% of mankind's energy consumption is for heating in winter. By halving this for homes and offices, a reduction of 40 million tons/year of _CO2 will be realized. It is also effective for moving objects such as automobiles and busses, further increasing the CO2 reduction effect. When the inventors conducted a heat insulation experiment in December using only a transparent super heat insulation film (without a light shielding film) as part of the JST commercialization development project development research, the room temperature did not drop below 20°C during daylight hours.

According to the invention, the shell 3 of the VO ₂ -loaded hollow particles 1 can be produced from a silica shell 6 and VO ions 9 . Therefore, the VO2 _- supporting hollow particles 1 having the shell ₃ having the VO2 particles 8 of 10 nm or less can be produced, and a VO2-supporting hollow particle film excellent in visible light transmittance can be provided.

A smart window has a method of adjusting the transparency of a material by voltage current in combination with a transparent electrode. Typical examples include those using liquid crystals and ionic conductors. Although this method has been put into practical use, it is expensive because the material is expensive and the manufacturing process is complicated. Also, since it is not temperature responsive, it requires an electrical control device such as an artificial on/off or computer control.

On the other hand, thermochromics of organic complexes are famous. Many molecules have been reported. For example, the N,N-diethylethylenediamine complex of copper [Cu(dieten)2](ClO4)2 changes its transmittance at 42°C. As can be seen from the fact that an erasable ballpoint pen is one of the thermochromic materials, inexpensive thermochromic materials have also come to appear on the market. There is also an example of application as a film for smart windows, but because it is an organic molecule, there is a problem with weather resistance, and it has not spread. However, since ON/OFF is performed by temperature, an electric control device can be dispensed with.

According to the VO ₂ -supported hollow particles 1 of the present invention, the VO ₂ particles 8 can be dispersedly present by being supported on the hollow particles, and the transparency of the nano-hollow particles does not impair the visibility of the window. In addition, it is possible to reduce the power consumption of air conditioners due to the heat insulating effect of the nano-hollow particles. Since the installed capacity of solar panels has exceeded 5 kW, the feasibility of homes and offices that can realize net zero energy is increasing. Taking an office building as an example, it is important to reduce energy consumption by introducing energy-saving products for lighting and OA equipment after improving the performance of the building's outer skin through heat insulation. In order to realize "net zero energy", the inventors have reduced energy consumption by putting into practical use the light management of highly heat-shielding and heat-insulating films through two types of energy-saving lighting using nano-hollow particles as a key technology. and contribute to _CO2 reduction.

1 VO ₂ -supported hollow particle 3 shell 5 core-shell particle 6 silica shell 7 template (PAA aggregate)
₈ VO2 particles 9 VO ions 10 Dispersion liquid 20 VO2 _- supporting hollow particle film 30 Window glass 33 Indoors 35 Outdoors

Claims (3)

A dispersion liquid (10) having polyacrylic acid aggregates and VO ions (9) as a hollow particle template (7) is stirred,
Tetraethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, dimethyltrimethoxysilane, dimethyltriethoxysilane, tetrachlorosilane or water glass is dropped into the dispersion,
Core-shell particles (5) in which a silica shell (6) is formed on the surface of the polyacrylic acid aggregate and the VO ions (9) are present at the interface between the polyacrylic acid aggregate and the silica shell (6) to generate
The core-shell particles ( 5) to generate
The template (7) is discharged by washing the core-shell particles (5) with water,
retaining the water inside;
Furthermore, the water inside is evaporated by heat treatment in an inert atmosphere,
A method for producing VO ₂ -supported hollow particles (1) having a shell (3) in which VO ₂ particles (8) in which the VO ions (9) are oxidized are supported on the silica shell (6). The method for producing VO2 _- supporting hollow particles ( ₁ ) according to claim 1, wherein the VO2 particles (8) have an outer diameter of 10 nm or less. VO ₂ -supported hollow particles (1) having a silica shell (3) supporting VO ₂ particles (8) and having an outer diameter of 10 to 100 nm,
VO ₂ -supported hollow particles (1), characterized in that the VO ₂ particles (8) having thermochromic properties have an outer diameter of 1 nm or less.

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