CN115703933B

CN115703933B - Nanoparticle, preparation method thereof and application of nanoparticle in heat insulation coating

Info

Publication number: CN115703933B
Application number: CN202210924699.5A
Authority: CN
Inventors: 杨晶磊; 罗文君; 张伟滨
Original assignee: Hong Kong University of Science and Technology HKUST
Current assignee: Hong Kong University of Science and Technology HKUST
Priority date: 2021-08-03
Filing date: 2022-08-02
Publication date: 2023-07-07
Anticipated expiration: 2042-08-02
Also published as: CN115703933A

Abstract

The present invention relates to a hollow-structured nanoparticle comprising an outer shell formed of silica nanoparticles and an inner shell formed of plasmonic nanoparticles, a method for the preparation thereof and the use thereof in coating compositions. The insulating glass coated with the coating composition of the present invention is capable of blocking at least 98% of ultraviolet light and at least 90% of near infrared light, and has a visible light transmittance of not less than 70%.

Description

Nanoparticle, preparation method thereof and application of nanoparticle in heat insulation coating

Technical Field

The invention relates to the field of coatings, in particular to a nanoparticle with a hollow core-shell structure, which comprises an outer shell formed by silica nanoparticles and an inner shell formed by plasma nanoparticles, a preparation method thereof and application thereof in heat insulation coatings.

Background

The heat-insulating coating can effectively prevent heat from sunlight penetrating through a window of a building, thereby reducing indoor environment temperature. Conventional insulating coatings are used to insulate by reducing the amount of heat transferred from the exterior surface to the room, and such insulating coatings are based primarily on materials of low thermal conductivity such as ceramic particles and polymer resins. The transparent heat-insulating coating is coated on the glass window, and can strongly shield near infrared and ultraviolet rays, so that solar heat absorbed by the window is greatly reduced, and the method has been widely explored and applied in the aspect of building energy conservation. The thermal insulation properties of architectural windows have gradually attracted considerable attention in energy saving applications, contributing significantly to a 10% to 30% reduction in annual cold load in summer for individual climate zones.

The existing heat-insulating coating mainly consists of a polymer matrix and an incorporated inorganic filler, and has limited absorption band in the Near Infrared (NIR) region. In recent years, with the rapid development of research and synthesis technology of nano materials, various nano particles and hollow particles gradually appear, and the development of heat insulation coating is promoted.

U.S. patent No. 10913858B2 discloses a water-based heat insulating coating material in which silica is uniformly dispersed in a resin as a heat insulating agent by a sol-gel method to eliminate the problem that particles are aggregated to form coarse particles, thereby simplifying the preparation process and preventing the influence of dispersion unevenness. Due to the good fineness of the silica dispersion, and 30.1m ² /g to 100m ² The coating layer formed by the water-based heat-insulating coating has compact structure, smooth surface and high surface reflectivity of more than 85 percent when being applied to the building surface. Such a coating can effectively block infrared rays and provide excellent heat insulating effect, dirt resistance and durability.

U.S. patent No. 20160160053A1 discloses a method of making and using a nanocomposite for coating glass, the nanocomposite consisting of a first metal oxide bridging a silicone oil moiety and an anionic surfactant moiety, and a second metal oxide bonded to the silicone oil moiety. The composite material may be manufactured by heating the first and second metal oxides with silicone oil and then adding a mixture of a surfactant and an oxidizing solution. Glass coated with such a composite material may transmit visible light, absorb some ultraviolet light, and reflect some near infrared light. The optical properties of the coated glass can be used to reduce the amount of heat in the enclosed region of the glass by reducing the amount of infrared and ultraviolet light transmitted through the glass. Although the adhesion between the coating and the glass substrate is improved, the complex synthesis steps make it difficult to apply to large area surfaces.

U.S. patent No. 4510190 discloses a transparent insulating coating that is neutral in terms of transmittance and appearance for insulating glass sheets. The coating is formed from a bismuth oxide-silver-bismuth oxide multilayer system in which a more electronegative substance (i.e., a substance having a higher standard potential) is added to the bismuth oxide layer to avoid blackening under ultraviolet radiation. The bismuth oxide layers act as reflection reducing layers in a multilayer system, i.e. they significantly increase the transmittance in the visible region. Such bismuth oxide-silver-bismuth oxide multilayer systems are capable of forming excellent thermal barrier coatings on glass substrates due to the appropriate layer thicknesses.

U.S. patent No. 5099621a relates to the use of conductive polymer materials to selectively control light transmittance through a transparent or translucent plate or film according to wavelength; and more particularly to the use of conductive polymer materials to provide shades having high transmittance in the visible range and high reflectance and absorptivity in the near and far infrared ranges. The coating solution can be readily applied to the substrate by a variety of low cost and effective methods known in the art, such as spin coating, spray coating, dip coating, or extrusion coating. The cost of the insulating window unit is significantly reduced, the manufacturing process is simplified, and the reliability and operating efficiency of the unit are improved.

U.S. patent No. 20130168595A1 relates to a nano heat insulating coating and a preparation method thereof, and more particularly to a blended solid solution of nano antimony tin oxide and nano vanadium oxide. The method comprises the following steps: mixing and stirring nano metal oxide and stirring auxiliary stirring liquid to form a mixed paste, filtering and drying the mixed paste to form a dried mixed block; calcining the dried mixed block to form an oxide solid solution block of metal oxide/silicon oxide; adding dispersion-assisting liquid and mixing-assisting liquid, mixing and then mechanically stirring, carrying out ultrasonic resonance and high-pressure homogenization to form the heat-insulating coating which is suitable for being coated on glass to achieve a heat-insulating special effect. Such a preparation process is not only time consuming but also more costly to manufacture, since the calcination and homogenization processes require extremely high temperatures and pressures, respectively.

U.S. patent No. 20120121886A1 discloses an infrared reflective coating composition comprising polymeric hollow particles, pigment particles, and at least one polymeric binder. The volume average particle size of the polymer hollow particles is 0.3 to 1.6 microns, which is significantly larger than that of conventional nanoparticle fillers. The coating composition is suitable for many applications, such as exterior construction or industrial applications. The invention also provides a coating material comprising at least one coating film derived from the coating composition. In architectural applications, the coating composition is suitable for coating exterior glazing surfaces. The coating composition applied to the substrate may be dried or allowed to dry over a wide temperature range of 1 ℃ to 95 ℃.

U.S. patent No. 20200239726A1 discloses an alkyd-containing polymer dispersion dispersed in water for use in forming a primary aqueous coating composition. The resulting aqueous coating composition comprises from about 2 to about 30 weight percent of one or more insulating fillers, with the remainder being an alkyd-containing dispersion, such that the coating composition contains from about 30 to about 80 weight percent water and from about 2 to about 50 weight percent alkyd-containing polymer. The coating formed from the coating composition exhibits heat resistance and a thermal conductivity of less than 100 mW/mK.

U.S. patent No. 8304099B2 and U.S. patent No. 8986851B2 disclose a composition and method of making a transparent thermal insulation material formed of tungsten oxide co-doped with metal cations and halogen anions, the transparent thermal insulation material being formed of M _x WO _y A _z Wherein M is at least one element of an alkali metal, and A is halogen. The transparent insulating material has a visible light transmittance of greater than about 70% and an infrared light shielding rate of greater than about 70%. The transparent heat insulating film of the present invention can enhance heat insulating ability and maintain the same level of visible light transmittance as the conventional film, compared to the conventional transparent heat insulating film containing undoped tungsten oxide or tungsten oxide doped with metal ions. However, the introduction of halogen elements can pose potential hazards to the surrounding environment and the human body.

U.S. patent No. 7252785B2 discloses a composition for producing a thermal barrier coating comprising at least one radiation absorbing compound and at least one IR reflecting component. The IR reflecting properties are due to the fact that after the IR reflecting component is oriented and cured, at least a portion of the oriented cholesteric polymer or at least a portion of the oriented polymer obtainable by polymerization of the monomer has a helical superstoid pitch corresponding to a wavelength in the infrared spectral range. It is known to use materials that reflect thermal radiation significantly for thermal insulation, in particular for shielding thermal radiation in the wavelength range 800nm to 2000 nm. In this invention, curing refers to polymerization of monomers and crosslinking of five polymers. Thus, while these compositions are known to provide insulating properties upon curing, their solvent sensitivity, flexibility and scratch resistance are not ideal.

Currently, a common feature of most existing methods for producing infrared and ultraviolet shielding coatings for thermal insulation purposes is the application of a hybrid coating comprising ceramic nanofillers, hollow particles, aqueous or solvent-based resins and coating aids via conventional coating processes such as spray, dip and deposition methods. However, in addition to the white and visible thickness of the coating, the lack of the ability to specifically block NIR light also limits further use of such products. Over the last decades, efforts have been directed to developing hybrid paint technology and its applications, which have also attracted increased attention in the building and construction materials field.

However, as disclosed in various documents and patents, some nano-inorganic particles and hollow particles, such as silica, hollow silica, calcium oxide, etc., do provide a certain shielding and reflecting effect for UV light and NIR light, and thus can effectively insulate a part of heat energy from sunlight. However, common nanomaterials used for thermal insulation purposes only interact with NIR light in a limited wavelength range and also reflect part of the visible light. For example, inorganic nanoparticles having a strong infrared absorption capability are mainly indium-based conductive oxides, but they exhibit excellent shielding properties only at wavelengths greater than 1500 nm.

Accordingly, there remains a great need in the art for thermal barrier coatings having excellent absorption/blocking capabilities in the Near Infrared (NIR) region.

Disclosure of Invention

As previously mentioned, the insulating properties of architectural windows have attracted considerable attention in energy saving applications. The main object of the present invention is to disclose a coating composition which, when applied as a coating to a glass surface, is capable of selectively absorbing almost all of the NIR and UV in the solar spectrum and maintaining a high visible light transmittance. The present inventors found that a coating composition is produced by combining or surface-modifying plasmonic nanoparticles to form a nanoparticle having a hollow core-shell structure, and then combining it with an aqueous resin or the like, and thus the produced coating exhibits excellent properties in terms of near infrared light/ultraviolet light blocking, uniformity, leveling, coatability, applicability, and the like, thereby leading to the present invention.

Accordingly, in a first aspect of the present invention, there is provided a nanoparticle having a hollow core-shell structure comprising an outer shell formed of silica nanoparticles and an inner shell formed of first plasmonic nanoparticles.

In a second aspect, there is provided a method of preparing the nanoparticle of the first aspect, comprising:

1) And a primary coating step: coating the substrate microsphere with the plasma nanoparticle to form a substrate @ plasma nanoparticle core-shell microsphere;

2) And a secondary coating step: coating the substrate @ plasma nanoparticle core-shell microspheres with silica nanoparticles to form substrate @ plasma nanoparticle @ silica nanoparticle core-shell microspheres;

3) And (3) calcining: calcining at 400-600 deg.c to eliminate the matrix microsphere and obtain nanometer microsphere with hollow core-shell structure.

In a third aspect, there is provided a coating composition consisting of, based on the total weight of the coating composition:

(A) 50 to 75% by weight of an aqueous resin;

(B) 11 to 35 wt% nanoparticle slurry comprising the nanoparticle of the first aspect or the nanoparticle prepared by the method of the second aspect or a combination comprising at least two second plasmonic nanoparticles; and

(C) 4 to 15% by weight of auxiliaries.

In a fourth aspect, there is provided a thermal barrier comprising a transparent substrate and the coating composition of the third aspect applied to a surface of the transparent substrate.

In a fifth aspect, there is provided a method of preparing the coating composition of the third aspect, comprising:

(1) Preparing nanoparticle slurry, wherein nanoparticles or at least two second plasma nanoparticles, a dispersing agent and a pH regulator are dispersed in deionized water, and stirring, ball milling and ultrasonic treatment are carried out to form nanoparticle slurry;

(2) Adding the obtained nanoparticle slurry into aqueous resin, and stirring to form an initial heat-insulating coating; and

(3) An auxiliary agent is added to the initial insulating coating to form a final coating composition.

The present invention provides a coating composition having excellent near infrared/ultraviolet blocking properties. The inventor finds that the combination of at least two plasma nanoparticles capable of absorbing different wavelength ranges is used, or the surface of the plasma nanoparticles is modified to form nano microspheres with hollow core-shell structures together with silicon dioxide, the plasma resonance effect on the surfaces of the plasma nanoparticles and the hollow cavity structures of the microspheres enable the obtained nanoparticles to have excellent near infrared blocking performance and high visible light transmittance, so that the organic-inorganic blending coating can absorb almost all ultraviolet light and near infrared light with a selected wavelength (wavelength higher than 780 nm) for heat insulation, can maintain the visible light transmittance of the coating, has the potential of being applied to building windows and curtain walls, and provides an ideal potential candidate material for building energy conservation.

The insulating glass coated with the coating composition of the present invention can absorb not less than 98% of ultraviolet light and not less than 70%, even not less than 90% of near infrared light, and has a visible light transmittance of at least 70%, thereby enabling the indoor and outdoor temperature differences of buildings of 8 to 10 ℃. Thus, the coating composition and insulating glass of the present invention can contribute significantly to a 10% to 30% reduction in the cooling load throughout the summer season in subtropical climates.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.

FIG. 1 shows plasmonic nanoparticles ATO, ITO and Cs _x WO ₃ Transmittance curves in the ultraviolet visible and infrared spectral ranges.

Fig. 2 shows a flowchart for preparing a nanoparticle having a hollow core-shell structure according to an embodiment of the present invention.

FIG. 3 shows a nanoparticle prepared according to one embodiment of the present invention: (a) Scanning Electron Microscope (SEM) images of ato@mesoporous silica nanoparticles in a broken state and (b) ito@mesoporous silica nanoparticles in a complete state; and (c) ATO@mesoporous silica nanoparticle in an intact state and (d) Transmission Electron Microscopy (TEM) image of ITO@mesoporous silica nanoparticle in an intact state.

Fig. 4 shows a flow chart of preparing a coating composition according to one embodiment of the invention.

FIG. 5 shows a 3mm uncoated glass and coated with coating compositions 1-3 prepared according to one embodiment of the invention (coating composition 1 comprising nanoparticle ATO, coating composition 2 comprising nanoparticle ATO and ITO, coating composition 2 comprising nanoparticle ATO, ITO and Cs, respectively _x WO ₃ The ultraviolet visible and near infrared transmittance curves of the 3mm insulating glass of coating composition 3).

FIG. 6 shows the ultraviolet visible and near infrared transmittance curves for 3mm uncoated glass and 3mm insulating glass coated with coating compositions 4-5 (coating composition 4 comprising ATO@mesoporous silica nanospheres, coating composition 5 comprising ITO@mesoporous silica nanospheres, respectively) prepared according to one embodiment of the invention.

FIG. 7 shows (a) a self-made simulated insulation test apparatus for testing insulating glass made in accordance with one embodiment of the present invention; and (b) temperature dependence of 3mm uncoated glass, (c) coated with coating composition 3, (d) coated with coating composition 4, and (e) 3mm insulating glass coated with coating composition 5 on irradiation time.

FIG. 8 shows the results of transmittance tests for (a) 3mm uncoated glass, (b) 3mm insulating glass coated with coating composition 3 and (c) 3mm insulating glass coated with coating composition 5, at 365nm ultraviolet wavelength and 1400nm near infrared wavelength, respectively, and in the visible light band 380-760nm region.

Detailed Description

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the following description is intended to illustrate the invention by way of example only, and is not intended to limit the scope of the invention as defined by the appended claims. And, it is understood by those skilled in the art that modifications may be made to the technical scheme of the present invention without departing from the spirit and gist of the present invention. The technical means used in the examples are conventional means well known to those skilled in the art unless otherwise indicated.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter described herein belongs. Before describing the present invention in detail, the following definitions are provided to better understand the present invention.

Where a range of values is provided, such as a range of concentrations, a range of percentages, or a range of ratios, it is to be understood that each intervening value, to the tenth of the unit of the lower limit, between the upper and lower limit of the range, and any other stated or intervening value in that stated range, is encompassed within the subject matter unless the context clearly dictates otherwise. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and such embodiments are also included in the subject matter, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the subject matter.

In the context of the present invention, many embodiments use the expression "comprising", "including" or "consisting essentially/mainly of … …". The expression "comprising," "including," or "consisting essentially of … …" is generally understood to mean an open-ended expression that includes not only the individual elements, components, assemblies, method steps, etc., specifically listed thereafter, but also other elements, components, assemblies, method steps. In addition, the expression "comprising," "including," or "consisting essentially of … …" is also to be understood in some instances as a closed-form expression, meaning that only the elements, components, assemblies, and method steps specifically listed thereafter are included, and no other elements, components, assemblies, and method steps are included. At this time, the expression is equivalent to the expression "consisting of … …".

For a better understanding of the present teachings and without limiting the scope of the present teachings, all numbers expressing quantities, percentages or proportions used in the specification and claims, and other numerical values, are to be understood as being modified in all instances by the term "about" unless otherwise indicated. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

In a first aspect of the present invention, there is provided a nanoparticle having a hollow core-shell structure comprising an outer shell formed of silica nanoparticles and an inner shell formed of first plasmonic nanoparticles.

In a specific embodiment, the silica nanoparticle is a mesoporous silica nanoparticle.

In the context of the present invention, the term "plasmonic nanoparticle" refers to a metal-containing nanoparticle capable of localized surface plasmon resonance. When sunlight is incident on the nano particles, if the frequency of the incident photons is close to the electron vibration frequency of the metal particles, a localized surface plasmon resonance phenomenon can occur. At this time, the metal nanoparticles have a strong interaction with photons of this frequency, exhibiting a selective blocking (absorption or reflection) of energy of a specific wavelength of the spectrum. The resonance wavelength of the nanoparticle depends on factors such as composition, shape, structure, size, etc. of the nanoparticle, so that the plasma nanoparticle conforming to the target properties can be prepared by varying experimental parameters.

In the context of the present invention, the term "mesoporous" refers to pores having a pore diameter of from 2nm to 50 nm.

In the context of the present invention, the expressions "first" and "second" in the terms of "first plasmonic nanoparticle" and "second plasmonic nanoparticle" are for distinguishing purposes only and are not intended to limit any order, or importance.

In yet another specific embodiment, the first plasmonic nanoparticle is Indium Tin Oxide (ITO), antimony Tin Oxide (ATO), lanthanum hexaboride (LaB) ₆ ) Cesium tungsten bronze (Cs) _x WO ₃ )(0＜x＜0.33)。

In a preferred embodiment, the first plasmonic nanoparticle is Indium Tin Oxide (ITO).

In yet another specific embodiment, the nanoparticle may have a size of 100nm to 500nm.

In a preferred embodiment, the nanoparticle may be 450 nanometers in size.

In yet another specific embodiment, the thickness of the housing may be 10nm to 20nm.

In a preferred embodiment, the thickness of the housing may be 15 nanometers.

In yet another specific embodiment, the thickness of the inner shell may be 15 nm to 30 nm.

In a preferred embodiment, the thickness of the inner shell may be 20 nanometers.

In a specific embodiment, the primary coating step comprises: and coating the substrate microsphere with the plasma nanoparticle by using the plasma metal salt precursor as a template through a sol-gel method. Here, the solvent-gel method is a common method for preparing molecular to nanostructural materials, which is well known in the art.

In further specific embodiments, the matrix microspheres may be polymeric microspheres, such as, but not limited to, polystyrene microspheres, polyethylene microspheres, polypropylene microspheres, and polyethylene terephthalate microspheres.

In a still further specific embodiment, the size of the matrix microsphere is 20 nm to 200 nm, preferably 100 nm. By selecting matrix microspheres (such as polystyrene microspheres) with different particle sizes as a template agent, the size-controllable nano microsphere with a hollow core-shell structure can be prepared by a sol-gel method.

In yet another specific embodiment, the plasmonic metal salt precursor is a halogen salt, nitrate salt, or combination thereof of plasmonic metal. One skilled in the art can select the appropriate plasmonic metal salt precursor depending on the plasmonic nanoparticle desired to be prepared. For example, when the first plasmonic nanoparticle is ATO, the plasmonic metal salt precursor used to prepare it may be SnCl ₂ Or a hydrate thereof and SbCl ₃ Or a hydrate thereof. When the first plasmonic nanoparticle is ITO, the plasmonic metal salt precursor used to prepare it may be In (NO ₃ ) ₃ Or a hydrate thereof and SnCl ₄ Or a hydrate thereof.

After the primary coating step is completed, the size of the matrix @ plasma nanoparticle core-shell microsphere is 40-300 nanometers.

In yet another specific embodiment, the primary coating step is performed at a pH of 7 to 13. In a preferred embodiment, the primary coating step is performed at a pH of 10. In this step, the pH may be adjusted by ammonia, sodium hydroxide, or the like.

In yet another specific embodiment, the secondary coating step comprises: and (3) performing secondary coating on the matrix @ plasma nanoparticle core-shell microsphere by using hexadecyl trimethyl ammonium bromide or P123 as a template agent and using tetraethyl orthosilicate through a sol-gel method to form the matrix @ plasma nanoparticle @ silicon dioxide nanoparticle core-shell microsphere. P123 is a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

After the secondary coating step is completed, the thickness of the silica nanoparticle layer in the matrix @ plasma nanoparticle @ silica nanoparticle core-shell microsphere is 10-20 nanometers.

In a preferred embodiment, the templating agent is removed by calcination in the calcining step.

In yet another specific embodiment, the secondary coating step is performed at a pH of 7 to 10. In a preferred embodiment, the preferred secondary coating step is performed at a pH of 8. In this step, the pH can be adjusted by adding ammonia, sodium hydroxide, etc. in a certain ratio.

In yet another specific embodiment, the temperature suitable for the calcination step may be selected based on the matrix microspheres, e.g. for polystyrene microspheres calcination is preferably performed at a temperature of 500 ℃.

In a third aspect, the present invention provides a coating composition consisting of, based on the total weight of the coating composition:

(A) 50 to 75% by weight of an aqueous resin;

(C) 4 to 15% by weight of auxiliaries.

In a specific embodiment, the aqueous resin is selected from at least one of an aqueous acrylic resin, a silicone modified acrylic resin, an aqueous polyurethane resin, and a fluorocarbon resin. The aqueous resin plays an important role in the film forming capability, flexibility, adhesion and the like of the coating.

In a preferred embodiment, the aqueous acrylic resin is an aqueous acrylic resin having a solids content of 20 to 60% by weight.

In yet another preferred embodiment, the silicone-modified acrylic resin is a silicone-modified acrylic resin having a solids content of 50 to 70 weight percent.

In still another preferred embodiment, the aqueous polyurethane resin is an aqueous polyurethane resin having a solid content of 30 to 50% by weight.

In yet another preferred embodiment, the fluorocarbon resin is a fluorocarbon resin having a solids content of 45 to 55 percent by weight.

In a more preferred embodiment, the fluorocarbon resin is a fluorocarbon resin having a fluorine content of 20 to 30 percent by weight.

In a specific embodiment, the second plasmonic nanoparticle is selected from Indium Tin Oxide (ITO), antimony Tin Oxide (ATO), vanadium dioxide (VO ₂ ) Vanadium pentoxide (V) ₂ O ₅ )、Cs _x WO ₃ (0 < x < 0.33), titanium dioxide (TiO) ₂ )、La _x Eu _1-x B ₆ (0 < x < 1). The present invention enables the coating composition of the present invention to achieve efficient absorption of selected near infrared wavelengths by selecting metal nanoparticles capable of supporting surface plasmon resonance. This resonance is a coherent oscillation of surface conduction electrons excited by electromagnetic radiation, by which photons of near infrared light interact with particles much smaller than the incident wavelength, creating a plasma that oscillates around the nanoparticle, accompanied by lightAbsorption or reflection.

For a combination of at least two second plasmonic nanoparticles, it may be for example a combination of ITO and ATO, ITO, cs _x WO ₃ Combinations of ATO and the like, but are not limited thereto. By combining resonance bands of different plasma nanoparticles, full blocking of certain wavelengths of light is achieved. FIG. 1 shows plasmonic nanoparticles ATO, ITO and Cs _x WO ₃ A transmission spectrum curve in the near infrared range of visible light. As can be seen from FIG. 1, cs _x WO ₃ The transmission peak in the visible region is narrower, but in the infrared region > 2000nm the transmittance gradually increases. Whereas ITO has a broad transmission peak in the 500nm to 1500nm range, it has very low transmittance in the infrared region > 1500 nm.

In the context of the present invention, the terms "transmittance" and "transmittance" are used interchangeably to characterize the extent of exit of incident light after refraction through an object. Accordingly, the phrase "visible light transmittance" or "visible light transmittance" as used herein characterizes the light transmission properties of an object in terms of the ratio of the luminous flux of transmitted visible light to the incident luminous flux.

In yet another specific embodiment, the second plasmonic nanoparticle has a particle size in the range of 100nm to 400nm.

When the nano microsphere with the hollow core-shell structure is used in the coating composition, the mesoporous SiO with low heat conductivity coefficient is adopted in the nano microsphere ₂ As a heat-resistant shell material, not only can the heat transfer between the plasma nanoparticles and the substrate, such as film, glass, in the hollow core-shell structure be slowed down, but also the shell/hollow structure formed is beneficial to reflecting more sunlight through multiple interfaces. Therefore, compared with the combination of the plasma nano particles, the nano microsphere with the hollow core-shell structure is obtained by carrying out surface modification on the plasma nano particles, so that the original optical properties of the plasma nano particles are maintained, and the blocking effect on sunlight, especially near infrared light in the sunlight, is also obviously improved.

In yet another specific embodiment, the nanoparticle slurry is a mixture of the nanoparticle or the combination of the at least two second plasmonic nanoparticles dispersed in water, such as deionized water, containing a dispersant and a pH adjuster.

In a preferred embodiment, the total weight of the nanoparticle or the second plasmonic nanoparticle is 20 wt% to 40 wt% of the total weight of the nanoparticle slurry.

In yet another specific embodiment, the dispersant is selected from polyvinylpyrrolidone, polyethylene glycol, or a combination thereof. The dispersant is used to bridge the space between the nanoparticles.

In yet another specific embodiment, the dispersant is 1 wt% to 3 wt% of the total weight of the nanoparticle slurry.

In yet another specific embodiment, the pH adjuster may be selected from hydrochloric acid or ammonia solution for increasing particle stability such that the pH of the nanoparticle slurry is 7 to 8.

In a preferred embodiment, the pH adjuster is 0.1 to 0.5 wt% of the total weight of the nanoparticle slurry.

In yet another specific embodiment, the auxiliary agents may include ultraviolet absorbers, leveling agents, defoamers, and film formers.

In a preferred embodiment, the uv absorber may be a compound comprising phenyl and/or c=n groups to block uv light and retard photo-oxidation of the coating compound. Those skilled in the art will appreciate that most of the plasmonic nanoparticles employed in the present invention do not have the ability to absorb ultraviolet light and that the coating composition of the present invention isolates substantially all ultraviolet light, such as at least 98% of the ultraviolet light, by adding an ultraviolet light absorber thereto.

In a more preferred embodiment, the ultraviolet absorber may be selected from at least one of benzophenone-based, benzotriazole-based, triazine-based, salicylate-based organic materials. The conjugated pi-electron structure in the uv absorber is responsible for the ability of the material to absorb uv. For example, ultraviolet absorbers contain, for example, ortho-hydroxyl groups, which form chelate rings with nitrogen or oxygen. Under the illumination effect, the energy absorbed by opening the chelate ring is just similar to the energy of ultraviolet light with the wave band of 290nm to 400nm, so that the aim of absorbing the ultraviolet light can be fulfilled.

Thus, in a more specific embodiment, the ultraviolet light absorber is one or more selected from the group consisting of bis (1, 2, 6-pentamethyl-4-piperidinyl) -sebacic acid ester of formula (I) below, benzotriazole of formula (II) below, 2-hydroxy-4 methoxybenzophenone of formula (III) below, and N- (ethoxycarbonylphenyl) -N' -methyl-phenyl formamidine of formula (IV) below.

In yet another preferred embodiment, the leveling agent may be selected from at least one of an acrylate copolymer and a non-reactive polyether modified polysiloxane for eliminating various possible defects of the coating during application.

In still another preferred embodiment, the defoamer may be selected from at least one of polysiloxane-polyether copolymer, octanol, tributyl phosphate, triphenyl phosphate, and emulsified methyl siloxane for eliminating bubbles generated during the preparation of the coating.

In yet another preferred embodiment, the film former may be selected from at least one of glycol ether solvents, glycol ester solvents, and dipropylene glycol butyl ether for promoting film formation and preventing cracking and breakage of the dry coating during curing.

In a more preferred embodiment, the uv absorber, the leveling agent, the defoamer, and the film forming agent may be 1 to 10 wt%, 0.01 to 1 wt%, and 0.5 to 3 wt%, respectively, based on the total weight of the coating composition.

By using surface modified plasmonic nanoparticles or a combination of plasmonic nanoparticles of a specific type in the coating composition of the invention, not only can light in the near infrared region wavelength range be selectively absorbed for heat insulation while maintaining the visible light transmittance of the coating, thereby ultimately imparting excellent heat insulation properties to architectural windows and curtain walls.

In a specific embodiment, the insulation is transparent.

In a preferred embodiment, the insulation has a visible light transmission of not less than 70%.

In a specific embodiment, the thickness of the coating composition applied to the surface of the transparent substrate is from 10 micrometers to 15 micrometers.

In a specific embodiment, the thermal shield absorbs at least 98% of the ultraviolet light.

In a preferred embodiment, the thermal shield absorbs at least 99% of the ultraviolet light.

In a specific embodiment, the thermal shield absorbs at least 70% of near infrared light.

In a further specific embodiment, the thermal shield absorbs at least 80% of near infrared light.

In a still further specific embodiment, the thermal shield absorbs about 90% of near infrared light.

In yet another embodiment, the transparent substrate is glass. The thermal insulation coating coated on the surface of the thermal insulation glass prepared by the method can absorb ultraviolet light with the solar spectrum not lower than 98 percent and even not lower than 99 percent and near infrared light with the solar spectrum not lower than 70 percent and even 90 percent, effectively shield heat, further effectively maintain indoor temperature, block or reduce the influence of environmental temperature, and realize the indoor and outdoor temperature difference of a building with the temperature ranging from 8 ℃ to 10 ℃. At the same time, the insulating glass has a visible light transmittance of at least 70% and thus has potential for application in architectural windows and curtain walls, thereby providing an ideal potential candidate for architectural energy conservation.

As described above, the heat insulating member achieves heat insulating properties mainly by selectively blocking/absorbing near infrared light in solar spectrum by the nano-microsphere having a hollow core-shell structure or the combination of at least two kinds of plasma nano-particles in the coating composition of the present invention coated on the surface of the transparent substrate. The insulation of the present invention can be manufactured at a low cost by a simple process well known to those skilled in the art. For example, the coating composition of the present invention can be applied to a large area substrate such as a glass substrate by a conventional coating process, and after curing, a uniform thermal barrier coating having a thickness of 10 to 15 μm is formed, which has a long service life, good stability, and easy maintenance, thereby achieving economic and social benefits due to the synergistic effect of the coating composition.

(1) Preparing nanoparticle slurry, wherein at least one kind of plasma nanoparticles, a dispersing agent and a pH regulator are dispersed in deionized water, and the nanoparticle slurry is formed through stirring, ball milling and ultrasonic treatment;

It is noted that in preparing the coating composition, it is desirable to avoid directly mixing the undispersed nanoparticles with the aqueous resin, since the dispersibility of the nanoparticle slurry affects the overall properties of the final coating composition to a large extent, the nanoparticles must be prepared as a uniformly dispersed slurry and then mixed with the resin and the auxiliary agent to prepare the coating.

The order of addition of the various adjuvants is not critical, but the coating composition of the invention must have sufficient mechanical agitation time after addition of each adjuvant to ensure uniform mixing. The above preparation method of the present invention is a method for preparing a coating having good dispersibility and uniformity, which is well known in the art, in a series of steps.

Examples

In the examples described below, the inventors prepared coating compositions comprising nanospheres having a hollow core-shell structure and coating compositions comprising one, two and three plasmonic nanoparticles, respectively, and examined their related thermal insulation properties as glass coatings.

Unless otherwise indicated, all test procedures used herein were conventional, and all test materials used in the examples described below were purchased from a conventional reagent store, unless otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The foregoing summary of the invention and the following detailed description are only for the purpose of illustrating the invention and are not intended to limit the invention in any way. The scope of the invention is determined by the appended claims without departing from the spirit and scope of the invention.

Example 1: preparation and optical performance characterization of ATO@mesoporous nano silicon dioxide

Referring to fig. 2, an exemplary preparation flow of the ato@mesoporous nanosilica of hollow structure is as follows:

1. preparation of polystyrene @ ATO microspheres

10 g of polystyrene spheres, 9 g of ammonia water and 100 ml of ethanol were weighed into a three-necked flask, and a solution containing a plasma metal salt precursor SnCl was added ₂ ·2H ₂ O and SbCl ₃ The mixture of ethanol and catalyst was added dropwise to a three-necked flask and allowed to react at 80℃for 6 hours. After the reaction system is cooled to room temperature, centrifuging the obtained microsphere, washing with ethanol for three times, drying at 60 ℃ for 12 hours, and obtaining the polystyrene@ATO microsphere, collecting and standing for the next reaction.

2. Preparation of polystyrene @ ATO @ nanosilicon dioxide microspheres

10 g of polystyrene@plasma particle microspheres obtained in the first step are dispersed in a mixed solution of 40 ml of isopropanol and 10 ml of deionized water by ultrasonic, and ammonia water with a certain proportion is added to adjust the PH value to 8.0. Then, 0.1 g of cetyltrimethylammonium bromide was added, and after stirring and dissolution at 25℃1 ml of tetraethyl orthosilicate was added, and after 3 hours of reaction, the reaction was stopped. And drying the sample at 120 ℃ to obtain the polystyrene@ATO@nano silica microspheres.

3. Preparation of ATO@mesoporous nano silica hollow core-shell structure microsphere

Placing the powder in a muffle furnace and calcining at 500 ℃ to remove polystyrene and cetyltrimethylammonium bromide template agent, thus obtaining the ATO@mesoporous nano silica hollow core-shell structure microsphere.

4. And (3) carrying out structural characterization on the ATO@mesoporous nano silicon dioxide hollow core-shell structure microsphere obtained in the step (3).

Fig. 3 (a) shows the ato@mesoporous silica nanoparticle in a broken state (only for the purpose of illustrating the internal structure of the nanoparticle), and it can be observed that the shell thickness of the ato@mesoporous silica hollow core-shell structure microsphere prepared by the above method is clearly visible to naked eyes, and the roughness of the shell material surface is covered by mesoporous spherical particles of different sizes. From fig. 3 (c), it can be observed that the hollow core-shell structure microsphere of ato@mesoporous nano silica prepared by the above method has a hollow structure, and the core-shell structure is clear.

Example 2: preparation and optical performance characterization of ITO@mesoporous nano silicon dioxide

Referring also to fig. 2, an exemplary preparation flow of the hollow structured ito@mesoporous nano silica is as follows:

1. preparation of polystyrene@ITO microspheres

10 g of polystyrene beads, 9 g of ammonia water and 100 ml of ethanol were weighed into a three-necked flask, and a solution containing plasma metal salt precursor In (NO ₃ ) ₃ ·5H ₂ O and SnCl ₄ ·5H ₂ The mixture of O, ethanol and catalyst was added dropwise to a three-necked flask and allowed to react at 80℃for 6 hours. Cooling the reaction system to room temperatureAnd centrifuging the obtained microsphere, washing with ethanol for three times, drying at 60 ℃ for 12 hours, and obtaining the polystyrene@ITO microsphere, collecting and standing for the next reaction.

2. Preparation of polystyrene @ ITO @ nanosilicon dioxide microspheres

10 g of polystyrene@ITO microspheres obtained in the first step are dispersed in a mixed solution of 80 ml of isopropanol and 10 ml of deionized water by ultrasonic, and ammonia water with a certain proportion is added to adjust the PH value to 8.0. Then, 0.1 g of cetyltrimethylammonium bromide was added, and after stirring and dissolution at 25℃1 ml of tetraethyl orthosilicate was added, and after 3 hours of reaction, the reaction was stopped. And drying the sample at 120 ℃ to obtain the polystyrene@ITO@nano silica microspheres.

3. Preparation of ITO@mesoporous nano silicon dioxide hollow core-shell structure microsphere

And placing the powder in a muffle furnace and calcining at 500 ℃ to remove polystyrene and cetyltrimethylammonium bromide template agent, thus obtaining the ITO@mesoporous nano silica hollow core-shell structure microsphere.

4. And (3) carrying out structural characterization on the ITO@mesoporous nano silicon dioxide hollow core-shell structure microsphere obtained in the step (3) to obtain an SEM spectrogram shown in the figure 3 (b) and a TEM spectrogram shown in the figure (d).

From fig. 3 (b), it can be observed that the morphology of the ito@mesoporous nano silica hollow core-shell structure microsphere prepared by the method is in a complete spherical shape, the surface of the shell material is rough, and the shell material is covered by mesoporous spherical particles with different sizes. The structure of the ITO@mesoporous nano silica hollow core-shell structure microsphere can be observed to be in a hollow form according to the figure 3 (d), and the core-shell structure is obvious.

Example 3: preparation of coating compositions

With reference to the process flow set forth in fig. 4, exemplary coating compositions 1-5 of the present invention were prepared according to the concentrations and volumes of the individual components set forth in table 1 below.

First, starting from step 101, the nanoparticle (or combination of plasma nanoparticles) having a hollow core-shell structure, a dispersant, a pH adjuster, and deionized water are mixed and stirred for 30 minutes to 1 hour to form a mixed suspension.

Then, in step 102, the mixed suspension is dispersed by grinding the suspension at a speed of 500rpm for 24 hours and sonicating at an amplitude of 25% for 30 minutes, thereby forming a well-dispersed nanoparticle slurry.

Next, in step 103, the well-dispersed nanoparticle slurry is added to the aqueous resin and then thoroughly mixed at 600rpm to form the initial thermal insulation coating.

Finally, in step 104, a coating aid is added and mixed with the initial insulating coating at a rate of 1000 revolutions per minute to form a final transparent insulating coating that can be applied to the surface of the glass substrate.

Example 4: visible light transmittance of the coating composition

Coating compositions 1-5 prepared in example 3 were applied to the surface of a glass substrate to form a coating having a thickness of about 10-15 microns, resulting in corresponding insulating glasses 1-5.

The insulating glass was subjected to ultraviolet-visible-near infrared (UV-Vis-NIR) transmission spectroscopy by hitachi UH 4150. Using the integrating sphere detection mechanism, the wavelength range of the visible-near infrared (Vis-NIR) spectrophotometer is 200nm to 2600nm, with results see fig. 5 and 6.

As can be seen from fig. 5, the glass inner surface coating, whether it comprises only one kind of nanoparticles or two or three kinds of nanoparticles, has a visible light transmittance of not less than 60%. However, coating composition 1 comprising only one type of ATO nanoparticle still has a low transmission peak in the infrared spectrum range of 800-2600nm, while coating

compositions

2 and 3 comprising two or three types of nanoparticles have only 40% infrared light transmittance, exhibiting weak blocking ability to the near infrared spectrum.

As can be seen from fig. 6, the uv-vis and near-ir transmission spectra of the 3mm insulating glass coated with the coating composition 4 prepared in example 3 (coating composition comprising ato@mesoporous silica nanobeads) exhibited a blocking rate of at least 98% in the uv band of 200-400nm, a transmittance of at least 70% in the visible band of 400-800nm, and a blocking rate of at least 80% in the near-ir band of greater than 1200 nm; the uv-visible and near-ir transmission spectra of the 3mm insulating glass coated with coating composition 5 prepared in example 3 (coating composition comprising ito @ mesoporous silica nanospheres) exhibited at least 98% blocking in the uv band 200-400nm, at least 70% transmission in the visible band 400-800nm, at least 90% blocking in the near-ir band greater than 1000nm, both exhibiting a strong blocking capacity for the near-ir spectrum.

Example 5: thermal insulation properties of coating compositions

The heat insulating properties of the heat insulating glasses 3 to 5 prepared in example 4 of the present invention were studied by a homemade test device. As shown in fig. 7a, the test device consisted of a 250W infrared lamp (wavelength range 760nm to 3000 nm), an insulated chamber with two windows covered with replaceable glass, and a temperature data logger. The difference in temperature between the inside and outside of the heat-insulating chamber of the uncoated glass of 3mm and the heat-insulating glass 3-5 produced in example 4 was examined, respectively, and the results are shown in FIGS. 7 (b) -7 (e). The ultraviolet visible and near infrared blocking rate test was simultaneously performed on the uncoated insulating glass and the insulating

glasses

3 and 5 prepared in example 4 using an LS182 solar film tester, and the results are shown in fig. 8.

As shown in fig. 7 (b) and 7 (c), the temperature in the test chamber (3) was higher than the temperature of the common glass face (1) (outside the test chamber) and the temperature of the common glass face (2) (inside the test chamber) for the heat-insulating chamber (fig. 7 (b)) of the uncoated glass (common glass), so that the temperature in the test chamber (3) was at the highest, about 42 ℃. Whereas for insulating glass with coating composition 3 (fig. 7 (c)), the temperature of the test cavity (3) with the plain glass was much lower than the inside (5) and outside (4) of the surface of the insulating glass. And comparing the difference between the temperature in the insulating cavity of the insulating glass and the temperature in the insulating chamber of the uncoated glass is about 5 deg.c, which proves that the coating composition 3 of the present invention can exhibit excellent insulating properties when applied to the glass surface, can effectively maintain the indoor temperature, block or reduce the influence of ambient temperature, but the coating itself has an excessively high temperature, which means that there may be a risk of degrading the coating during the long-term use of the insulating glass, thereby affecting the service life of the coating.

As shown in fig. 7 (d) and 7 (e), for the glass insulation chamber coated with the coating composition 4 (fig. 7 (d)), the temperature in the test chamber (3) in which the ordinary glass was installed was approximated to the temperature of the coated glass face (4) (outside the test chamber) and the ordinary glass face (5) (inside the test chamber), and it was found by comparison that the difference between the temperature in the insulation chamber of the insulation glass and the temperature in the insulation chamber of the uncoated glass was about 6 ℃; for the insulating glass coated with the coating composition 5 (fig. 7 (e)), the temperature inside (5) and outside (4) of the surface of the insulating glass was lower than the temperature inside (3) of the test chamber in which the plain glass was installed, and it was found by comparison that the difference between the temperature inside the insulating chamber of the insulating glass and the temperature inside the insulating chamber of the uncoated glass was about 8.5 ℃. The data demonstrate that when the coating composition 4-5 of the invention is coated on the surface of glass, not only can excellent heat insulation performance be shown, but also the coating has better heat radiation performance, so that the service life of the heat insulation glass is greatly prolonged, and excellent market application potential is shown.

As shown in FIGS. 8 (a) -8 (c), for an ordinary uncoated glass having a thickness of 3mm (FIG. 8 (a)), it has a blocking ratio of 14.4% at 365nm, a transmittance of 88.9% at 400-800nm, and a blocking ratio of 17.7% at 1400 nm. The 3mm insulating glass coated with the coating composition 3 prepared in example 3 (fig. 8 (b)) had a blocking rate of 96.9% at 365nm of ultraviolet light wavelength, a transmittance of 79.9% at 400-800nm of visible light wavelength, and a blocking rate of 84.2% at 1400nm of near infrared wavelength, compared to the 3mm uncoated glass. However, a 3mm insulating glass (FIG. 8 (c)) coated with coating composition 5 prepared in example 3 (coating composition comprising ITO@mesoporous silica nanospheres) had a 98.4% barrier at 365nm wavelength of ultraviolet light, 78.1% transmission in the visible light band 400-800nm, 93.8% barrier at 1400nm near infrared wavelength, and the best choice was made for all coating compositions.

Claims

1. A nanoparticle having a hollow core-shell structure comprising an outer shell formed of silica nanoparticles and an inner shell formed of first plasmonic nanoparticles; wherein the first plasma nanoparticle is indium tin oxide ITO, antimony tin oxide ATO, lanthanum hexaboride LaB ₆ Cesium tungsten bronze Cs _x WO ₃ ，0 < x <0.33; the thickness of the shell is 10 nanometers to 20 nanometers; the thickness of the inner shell is 15 nm to 30 nm.

2. The nanoparticle of claim 1, wherein the silica nanoparticle is a mesoporous silica nanoparticle.

3. The nanoparticle of claim 1, wherein the first plasmonic nanoparticle is indium tin oxide, ITO.

4. The nanoparticle of any one of claims 1-3, wherein the nanoparticle is 100 nanometers to 500 nanometers in size.

5. The nanoparticle of any one of claims 1-3, wherein the nanoparticle is 450 nanometers in size.

6. The nanoparticle of any one of claims 1-3, wherein the shell has a thickness of 15 nanometers.

7. The nanoparticle of any one of claims 1-3, wherein the inner shell has a thickness of 20 nanometers.

8. A method of preparing the nanoparticle of any one of claims 1-7, comprising:

9. The method of claim 8, wherein the calcining step is performed at a temperature of 500 ℃.

10. The method of claim 8, wherein the primary coating step comprises: the substrate microsphere is used as a template, and plasma metal salt precursors are used for coating the substrate microsphere with the plasma nanometer particles through a sol-gel method.

11. The method of claim 10, wherein the matrix microspheres are polymeric microspheres selected from the group consisting of polystyrene microspheres, polyethylene microspheres, polypropylene microspheres, and polyethylene terephthalate microspheres.

12. The method of claim 10, wherein the plasmonic metal salt precursor is a halogen salt, nitrate salt, or combination thereof of plasmonic metal.

13. The method of any of claims 8-12, wherein the secondary coating step comprises: and (3) performing secondary coating on the matrix @ plasma nanoparticle core-shell microsphere by using hexadecyl trimethyl ammonium bromide or P123 as a template agent and using tetraethyl orthosilicate through a sol-gel method to form the matrix @ plasma nanoparticle @ silicon dioxide nanoparticle core-shell microsphere.

14. The method of claim 13, wherein the templating agent is removed by calcination in the calcining step.

15. The method according to any one of claims 8-12, wherein the primary coating step is performed at a pH of 7-13; the secondary coating step is carried out at a pH of 7-10.

16. The method of any one of claims 8-12, wherein the primary coating step is performed at a pH of 10.

17. The method of any one of claims 8-12, wherein the secondary coating step is performed at a pH of 8.

18. The method of any one of claims 8-12, wherein the size of the matrix microsphere is 20 nm to 200 nm.

19. The method of any one of claims 8-12, wherein the matrix microsphere has a size of 100 nanometers.

20. A coating composition, the coating composition consisting of, based on the total weight of the coating composition:

(A) 50 to 75% by weight of an aqueous resin;

(B) 11 to 35 wt% nanoparticle slurry comprising the nanoparticle of any one of claims 1-7 or the nanoparticle prepared by the method of any one of claims 8-19; and

(C) 4 to 15% by weight of auxiliaries.

21. The coating composition of claim 20, wherein the nanoparticle slurry is a mixture of the nanoparticles dispersed in water containing a dispersant and a pH adjuster.

22. The coating composition of claim 20 or 21, wherein the total weight of the nanoparticle is 20 to 40 weight percent of the total weight of the nanoparticle slurry.

23. The coating composition according to claim 20 or 21, wherein the aqueous resin is at least one selected from the group consisting of an aqueous acrylic resin, a silicone-modified acrylic resin, an aqueous polyurethane resin, and a fluorocarbon resin;

the aqueous acrylic resin is an aqueous acrylic resin with a solid content of 20 to 60 wt%;

the organic silicon modified acrylic resin is organic silicon modified acrylic resin with the solid content of 50 to 70 weight percent;

the aqueous polyurethane resin is an aqueous polyurethane resin with a solid content of 30 to 50 weight percent; and

the fluorocarbon resin is a fluorocarbon resin having a solid content of 45 to 55% by weight.

24. The coating composition of claim 23, wherein the fluorocarbon resin is a fluorocarbon resin having a fluorine content of 20 to 30 weight percent.

25. The coating composition of claim 21, wherein the dispersant is selected from polyvinylpyrrolidone, polyethylene glycol, or a combination thereof.

26. The coating composition of claim 25, wherein the dispersant is 1 to 3 weight percent of the total weight of the nanoparticle slurry.

27. The coating composition of claim 21, wherein the pH adjuster is selected from hydrochloric acid or an ammonia solution.

28. The coating composition of claim 27, wherein the pH adjuster is 0.1 to 0.5 wt% of the total weight of the nanoparticle slurry.

29. The coating composition of claim 20 or 21, wherein the nanoparticle slurry has a pH of 7 to 8.

30. A coating composition according to claim 20 or 21, wherein the auxiliary agent comprises an ultraviolet absorber, a levelling agent, a defoamer and/or a film former;

the ultraviolet absorber is a compound including a phenyl group and/or a c=n group;

the leveling agent is at least one selected from acrylate copolymer and nonreactive polyether modified polysiloxane;

the defoamer is at least one selected from polysiloxane-polyether copolymer, octanol, tributyl phosphate, triphenyl phosphate and emulsified methyl siloxane;

The film forming agent is at least one selected from glycol ether solvent, glycol ester solvent and dipropylene glycol butyl ether.

31. The coating composition of claim 30, wherein the ultraviolet absorber is selected from at least one of benzophenone, benzotriazole, triazine, salicylate organic compounds.

32. The coating composition of claim 30, wherein the amounts of the ultraviolet absorber, the leveling agent, the defoamer, and the film former are from 1 to 10 wt%, from 0.01 to 1 wt%, and from 0.5 to 3 wt%, respectively, based on the total weight of the coating composition.

33. A thermal insulation comprising a transparent substrate and the coating composition of any one of claims 20-32 applied to a surface of the transparent substrate.

34. The insulation of claim 33, wherein the transparent substrate is glass.

35. A thermal shield according to claim 33 or 34, wherein the thermal shield is transparent.

36. The insulation of claim 33 or 34, wherein the insulation has a visible light transmission of not less than 70%.

37. The insulation of claim 33 or 34, wherein the thickness of the coating composition applied to the surface of the transparent substrate is from 10 microns to 15 microns.

38. The insulation of claim 33 or 34, wherein the insulation absorbs at least 70% of near infrared light; and the thermal shield absorbs at least 98% of the ultraviolet light.

39. The insulation of claim 33 or 34, wherein the insulation absorbs at least 80% of near infrared light.

40. The insulation of claim 33 or 34, wherein the insulation absorbs at least 90% of near infrared light.

41. A thermal shield according to claim 33 or 34, wherein the thermal shield absorbs at least 99% of uv light.

42. A method of preparing the coating composition of any one of claims 20-32, comprising:

(1) Preparing nanoparticle slurry, wherein the nanoparticle slurry is formed by dispersing the nanoparticle of any one of claims 1-7 or the nanoparticle prepared by the method of any one of claims 8-19, a dispersing agent, and a pH adjuster in deionized water, stirring, ball milling, and ultrasonic treatment;