Alumina three-dimensional nanometer grid structure and preparation method and application thereof

Abstract

The invention provides an aluminum oxide three-dimensional nanometer grid structure and a preparation method and application thereof, and belongs to the technical field of nanometer structure materials. The aluminum oxide three-dimensional nano-grid structure provided by the invention comprises an aluminum oxide matrix with transverse and longitudinal three-dimensional interconnected pore structures and fillers filled in the transverse and longitudinal three-dimensional interconnected pore structures, the color and radiation cooling power are adjusted by storing and removing the filler in the pore channel structure. A series of transverse channels are selectively etched in a traditional porous anodic aluminum oxide template, a three-dimensional interconnected anodic aluminum oxide network is constructed, liquid or solid filler is filled and removed in the three-dimensional channels, and the periodic refractive index of the thin film structure is dynamically adjusted to achieve switchable optical and thermal properties, so that the performance of the thin film is improved. Therefore, the dynamic control of the color and the cooling power is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterials, and specifically relates to an aluminum oxide three-dimensional nano-grid structure and a preparation method and application thereof. Background Art

[0002] The radiation cooling technology based on nanophotonics is a technology that uses the physical mechanism of thermal radiation to transfer heat to the outer space environment to achieve passive cooling. However, when people try to apply radiation cooling technology to scenes such as buildings, vehicles, and daily clothing, they are restricted by the fact that the appearance color of most radiation cooling materials is usually white or silver, which seriously restricts its diversified expansion possibilities in terms of aesthetic design; at the same time, the high reflective properties of white or silver are prone to cause glare problems, which poses potential harm to the visual health of users. The current solutions mainly include the following aspects: First, construct a structure composed of multiple layers of dielectric films, such as using silicon oxide, silicon nitride, magnesium fluoride, silicon carbide and other films of different materials to stack, and use the reflection interference phenomenon between the interfaces of each layer of film to generate specific colors; second, design based on the principle of localized surface plasmon resonance, that is, embedding metal nanoparticles into the radiation cooling material system, and relying on the unique plasma resonance characteristics of metal nanoparticles in the visible band to make the material present a rich and diverse color appearance.

[0003] However, after the structure is manufactured, it is difficult to achieve in-situ dynamic switching of colors for structures composed of multiple layers of dielectric films and solutions based on localized surface plasmon resonance. In addition, the additional optical loss caused by localized surface plasmon resonance weakens the radiation cooling performance of the material, and cannot meet the needs of real-time adjustment of color and cooling according to environmental changes. Summary of the invention

[0004] The purpose of the present invention is to provide an aluminum oxide three-dimensional nano-grid structure and a preparation method and application thereof. The aluminum oxide three-dimensional nano-grid structure provided by the present invention can realize in-situ dynamic control of color and radiation cooling power.

[0005] In order to achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] An aluminum oxide three-dimensional nano-grid structure comprises an aluminum oxide matrix having a transverse and longitudinal three-dimensional interconnected pore structure and a filler filled in the transverse and longitudinal three-dimensional interconnected pore structure; the color and radiation cooling power are adjusted by storing and removing the filler in the pore structure.

[0007] Preferably, the filler is a liquid filler that does not chemically react with the alumina matrix;

[0008] Or a solid polymer filler having an infrared absorption peak chemical bond in the 8-13 μm wavelength band.

[0009] Preferably, the liquid filler includes one or more of water, alcohol reagents, and ketone reagents;

[0010] The solid polymer filler includes one or more of polydimethylsiloxane, polymethyl methacrylate, polyvinyl chloride, and polyphenylene ether resin.

[0011] Preferably, the pore spacing of the transverse pores of the alumina three-dimensional nanogrid structure is 150-620 nm, and the pore spacing of the longitudinal pores is 30-600 nm; the pore diameter of the transverse pores is 35-60 nm, and the pore diameter of the longitudinal pores is 40-200 nm.

[0012] The present invention also provides a method for preparing the alumina three-dimensional nanogrid structure of the above technical solution, including the following steps:

[0013] Subject the aluminum material to pulsed anodic oxidation to obtain a porous anodic alumina template with vertical pores;

[0014] Subject the porous anodic alumina template to transverse acid etching to obtain an alumina matrix with transverse and vertical pores;

[0015] Fill the pore structure of the alumina matrix to obtain the alumina three-dimensional nanogrid structure.

[0016] Preferably, the electrolyte for the pulsed anodic oxidation is a polyacid electrolyte.

[0017] Preferably, the voltage for the pulsed anodic oxidation is composed of an alternating low-field voltage and high-field voltage;

[0018] When the polyacid electrolyte is a sulfuric acid solution, the low-field voltage is 20-27 V, and the duration is 100-530 s; the high-field voltage is 32-40 V, and the duration is 2-5 s;

[0019] When the polyacid electrolyte is an oxalic acid solution, the low-field voltage is 40-47 V, and the duration is 100-530 s; the high-field voltage is 52-60 V, and the duration is 2-5 s;

[0020] When the polyacid electrolyte is a phosphoric acid solution, the low-field voltage is 195-202 V, and the duration is 100-530 s; the high-field voltage is 255-263 V, and the duration is 2-5 s;

[0021] The total time for the pulsed anodic oxidation is 2-36 h, and the temperature is 5-25 °C.

[0022] Preferably, the concentration of the polyacid electrolyte is 0.2 - 0.8 M.

[0023] Preferably, the reagent used for acid etching is a phosphoric acid solution with a concentration of 5 - 8 wt%;

[0024] The temperature of the acid etching is 30 - 60 °C, and the time is 10 - 40 min.

[0025] The present invention also provides an application of the alumina three-dimensional nanogrid structure described in the above technical solution or the alumina three-dimensional nanogrid structure prepared by the preparation method described in the above technical solution in buildings, transportation means or clothing with radiative cooling functions.

[0026] The present invention provides an alumina three-dimensional nanogrid structure, including an alumina matrix with a three-dimensional interconnected pore structure in the transverse and longitudinal directions and a filler filled in the three-dimensional interconnected pore structure in the transverse and longitudinal directions; by storing and removing the filler in the pore structure, the color and radiative cooling power are adjusted. The present invention has an alumina matrix with three-dimensional interconnection of pores in the transverse and longitudinal directions. This three-dimensional interconnected structure has the ability to store fillers. By storing and removing the fillers in the pores, the refractive index is periodically adjusted, showing an alternating arrangement of layers with different refractive indices in the transverse direction. This long-range ordered structure satisfies the Bragg reflection condition, and due to the ability to adjust the photonic bandgap, in-situ dynamic color switching can be achieved; at the same time, by storing and removing fillers in the transverse and longitudinal pores, the infrared spectral response is adjusted to realize the dynamic regulation of radiative cooling performance, breaking through the limitation that it is difficult to regulate after the structure is processed, and is suitable for applications in scenarios such as dynamic appearance and adjustable thermal response.

[0027] In addition, the alumina three-dimensional nanogrid structure of the present invention can be used as a dielectric film. Compared with other multi-layer metal materials, alumina has lower dielectric loss, thus significantly reducing optical loss and contributing to the improvement of radiative cooling efficiency; the preparation method of the alumina three-dimensional nanogrid structure of the present invention is more convenient, has lower cost, and can be prepared in large areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is a process flow chart for preparing an alumina three-dimensional nanogrid structure in a sulfuric acid electrolyte in Example 1; where a is the preparation flow chart, b is a schematic diagram of a pulsed anodic oxidation device, and c is a schematic diagram of a periodic pulsed voltage in pulsed anodic oxidation;

[0030] Figure 2 Functional diagram for color regulation of the alumina three-dimensional nanogrid structure obtained in Example 1; wherein, a is the visible spectrum performance when water is not filled, b is the visible spectrum performance after water is filled, c is the color display physical diagram when water is not filled, and d is the color display physical diagram in three states during the water filling process;

[0031] Figure 3 Process flow diagram for preparing the alumina three-dimensional nanogrid structure in an oxalic acid electrolyte in Example 2; wherein, a is the preparation flow diagram, b is the schematic diagram of the pulsed anodic oxidation device, and c is the schematic diagram of the periodic pulsed voltage in pulsed anodic oxidation;

[0032] Figure 4 Diagram of the radiative cooling performance test device; wherein, a is the physical diagram of the test device, and b is the schematic diagram of the specific design details of the measurement box;

[0033] Figure 5 Diagram of the infrared spectrum change and radiative cooling performance regulation effect of the alumina three-dimensional nanogrid structure obtained in Example 2 before and after water filling; wherein, a is the infrared spectrum change, and b is the radiative cooling performance regulation effect;

[0034] Figure 6 Process flow diagram for preparing the alumina three-dimensional nanogrid structure described in Example 3;

[0035] Figure 7 Infrared spectrum and radiative cooling performance diagram of the alumina three-dimensional nanogrid structure obtained in Example 3, wherein, a is the infrared spectrum, and b is the radiative cooling performance. Detailed implementation manner

[0036] The present invention provides an alumina three-dimensional nanogrid structure, including an alumina matrix having a three-dimensional interconnected pore structure in the transverse and longitudinal directions and a filler filled in the three-dimensional interconnected pore structure in the transverse and longitudinal directions; by storing and removing the filler in the pore structure, the color and radiative cooling power are adjusted.

[0037] In the present invention, without special instructions, all preparation raw materials are commercially available products well-known to those skilled in the art.

[0038] In the present invention, the filler is a liquid filler that does not chemically react with the alumina matrix; or a polymer filler having an infrared absorption peak chemical bond in the 8-13 μm band; the liquid filler is one or more of water, alcohol reagents, and ketone reagents; the water can be deionized water or pure water; the alcohol reagent can be methanol, ethanol, or propanol; the ketone reagent can be acetone; the solid polymer filler is one or more of polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polyphenylene ether resin (PPO).

[0039] The present invention has no special limitation on the filling amount of the filler. The filling amount in the present invention refers to all the capacities of the entire alumina three-dimensional nanogrid structure; the amount of the filled liquid filler or polymer filler will affect the color / power.

[0040] In the present invention, the transverse channels and the longitudinal three-dimensions of the alumina three-dimensional nanogrid structure are independent of each other and parallel to each other.

[0041] In the present invention, the pore spacing of the transverse channels of the alumina three-dimensional nanogrid structure is 150-620 nm. In specific embodiments, it can be 240, 320, or 460 nm; the pore spacing of the longitudinal channels is 30-600 nm. In specific embodiments, it can be 65, 100, or 350 nm; the pore diameter of the transverse channels is 35-60 nm. In specific embodiments, it can be 40 or 50 nm, and the pore diameter of the longitudinal channels is 40-200 nm. In specific embodiments, it can be 60, 80, or 120 nm.

[0042] In the present invention, the pore spacing and the pore diameter will affect the color switching effect in the present invention. For a specific specific structure, the changes in the pore spacing and the pore diameter will lead to changes in the porosity of the structure, and further lead to changes in the equivalent refractive index. According to the Bragg reflection formula, this change in the equivalent refractive index will bring about a change in the position of the center wavelength of the reflection peak in the reflection spectrum, and finally change the color of the sample.

[0043] The position of the reflection peak under this dynamic regulation is determined by Equation I:

[0044] Δn1t1 + Δn2t2 = mΔλ / 2, (m = 1, 2, 3,...) Equation I;

[0045] Wherein, Δn1 is the change in the equivalent refractive index of the part of the alumina three-dimensional nanogrid structure that only contains longitudinal channels, Δn2 is the change in the equivalent refractive index of the part of the alumina three-dimensional nanogrid structure that contains both transverse channels and longitudinal channels, and λ is the center wavelength of the reflection peak;

[0046] The calculation method of the equivalent refractive index of each part in the structure is shown in Equation II:

[0047]

[0048] In Formula II, is the refractive index of alumina, and n d is the refractive index of the filler; f is the porosity of the three-dimensional alumina nano-grid structure;

[0049] The calculation method of f is shown in Formula III:

[0050]

[0051] In Formula III, C = 0 corresponds to the porosity containing only the longitudinal pore part, and C = 1 corresponds to the porosity containing both the longitudinal and transverse pore parts. Among them, d is the pore diameter of the longitudinal pore, D int,long is the pore spacing of the longitudinal pore, D int,trans is the pore spacing of the transverse pore, t2 is the long diameter of the transverse pore, and a is the short diameter of the transverse pore.

[0052] According to Formula III, when other structural parameters are the same, the larger the longitudinal pore spacing, the larger the porosity (f) of the structure; according to Formula II, the change in porosity will affect the effective refractive index of each part in the structure, and then change the position of the Bragg reflection peak (Formula I), making the structure present different colors

[0053] The present invention also provides a preparation method of the three-dimensional alumina nano-grid structure described in the above technical solution, including the following steps:

[0054] Perform pulsed anodic oxidation on the aluminum material to obtain a porous anodic alumina template with vertical pores;

[0055] Perform transverse acid etching on the porous anodic alumina template to obtain an alumina matrix with transverse and vertical pores;

[0056] Fill the pore structure of the alumina matrix to obtain the three-dimensional alumina nano-grid structure.

[0057] In the present invention, the electrolyte for the pulsed anodic oxidation is a polyacid electrolyte; the polyacid electrolyte includes one of sulfuric acid solution, phosphoric acid solution, and oxalic acid solution; the concentration of the polyacid electrolyte is 0.2 - 0.8 M, and in specific embodiments, it can be 0.3 or 0.5 M.

[0058] In the present invention, the voltage of the pulsed anodic oxidation consists of alternating low-field voltage and high-field voltage; when the multi-acid electrolyte is sulfuric acid solution, the low-field voltage is 20 - 27V, and in specific embodiments, it can be 22V or 25V, and the duration is 100 - 530s, and in specific embodiments, it can be 180s, 240s, 360s or 480s; the high-field voltage is 32 - 40V, and in specific embodiments, it can be 32V or 38V, and the duration is 2 - 5s, and in specific embodiments, it can be 2s or 4s; when the multi-acid electrolyte is oxalic acid solution, the low-field voltage is 40 - 47V, and in specific embodiments, it can be 40V or 45V; the duration is 100 - 530s; the high-field voltage is 52 - 60V, and in specific embodiments, it can be 52V or 56V; the duration is 2 - 5s; when the multi-acid electrolyte is phosphoric acid solution, the low-field voltage is 195 - 202V, and the duration is 100 - 530s; the high-field voltage is 255 - 263V, and the duration is 2 - 5s; the total time of the pulsed anodic oxidation is 2 - 36h, and the temperature is 5 - 25°C.

[0059] In the present invention, cleaning the aluminum material is also included before the pulsed anodic oxidation; the reagents used for cleaning include potassium hydroxide solution and absolute ethanol; the concentration of the potassium hydroxide solution is 1 - 2M.

[0060] In the present invention, removing the unreacted aluminum material is also included after the pulsed anodic oxidation; the method for removing the unreacted aluminum material is: immersing the porous anodic aluminum oxide template into a mixed solution of copper chloride and hydrochloric acid; the concentration of copper chloride in the mixed solution is 1 - 5M; the concentration of hydrochloric acid is 0.1 - 0.5M.

[0061] In the present invention, the reagent used for acid etching is phosphoric acid solution, the concentration of the phosphoric acid solution is 5 - 8wt%, and in specific embodiments, it can be 5wt%; the temperature of the acid etching is 30 - 60°C, and in specific embodiments, it can be 45°C, and the time is 10 - 40min, and in specific embodiments, it can be 25min or 35min.

[0062] In the present invention, aluminum materials are subjected to periodic pulse anodic oxidation under low pressure and high pressure. The aluminum oxide generated during the high-pressure oxidation contains more impurities and has a lower density of aluminum oxide, resulting in a faster corrosion rate of this area in the subsequent acid etching step, thereby exposing the lateral pores and forming an interconnected three-dimensional structure. This three-dimensional interconnected structure has the ability to store and remove fillers, and realizes the periodic adjustment of the refractive index by storing and removing fillers. It shows an alternating arrangement of different refractive index layers longitudinally. This long-range ordered structure satisfies the Bragg reflection condition, and due to its ability to adjust the photonic bandgap, it can achieve in-situ dynamic color switching; at the same time, by storing and removing fillers in the lateral and longitudinal pores, the dynamic regulation of the radiative cooling performance can also be achieved by adjusting the infrared spectral response. Therefore, it is suitable for applications in scenarios such as dynamic appearance and adjustable thermal response.

[0063] The present invention has no special limitation on the filling method; when the filler is a liquid filler, a dropper is used to suck the liquid filler and drop it on the surface of the aluminum oxide matrix, or other containers are used to hold the liquid and directly pour or flow it onto the surface of the aluminum oxide matrix to make the liquid filler completely infiltrate the aluminum oxide matrix. When the filler is a solid filler, the filler initially enters the aluminum oxide matrix in a liquid state and is subsequently cured by natural solidification or heating; the present invention has no special limitation on the curing conditions.

[0064] The present invention also provides the application of the aluminum oxide three-dimensional nanogrid structure described in the above technical solution or the aluminum oxide three-dimensional nanogrid structure prepared by the preparation method described in the above technical solution in buildings, transportation tools or clothing with radiative cooling functions.

[0065] In order to further illustrate the present invention, the aluminum oxide three-dimensional nanogrid structure provided by the present invention, its preparation method and application will be described in detail below in conjunction with the drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0066] Example 1

[0067] According to Figure 1 the process flow chart shown, the aluminum oxide three-dimensional nanogrid structure is prepared, and the specific steps are as follows:

[0068] The aluminum foil with a purity of 99.95% is cut into aluminum sheets of 5 cm × 7 cm, and is successively placed in a potassium hydroxide solution with a concentration of 1 M and absolute ethanol for ultrasonic cleaning treatment to obtain pretreated aluminum sheets;

[0069] The above pretreated aluminum sheets were immersed in a sulfuric acid electrolyte with a concentration of 0.3 M, and pulsed anodic oxidation was carried out at 5 °C with the aid of a cooling circulating water device. During the process, a periodic pulsed voltage was applied. Specifically, low-voltage oxidation with an applied voltage of 25 V was carried out for a duration of 180 s, and high-voltage oxidation with an applied voltage of 32 V was carried out for a duration of 2 s. The two steps of low-voltage oxidation and high-voltage oxidation were carried out alternately for a total of 11 h. The aluminum sheets that completed pulsed anodic oxidation were immersed in a mixed acidic solution of 1 M copper chloride and 0.1 M hydrochloric acid to remove the remaining unreacted aluminum sheets, and a porous anodic aluminum oxide template with a vertical pore structure was obtained.

[0070] The above porous anodic aluminum oxide template was immersed in a phosphoric acid solution with a concentration of 5 wt%, and soaked in a heating environment at 45 °C for 25 min to create nano lateral pores with a lateral pore spacing of 65 nm and a pore diameter of 40 nm, obtaining an alumina matrix.

[0071] A dropper was used to suck deionized water and drop it onto the surface of the alumina matrix to make the deionized water completely infiltrate, obtaining an alumina three-dimensional nano grid structure.

[0072] As Figure 1 shown, by changing the duration of low-voltage oxidation (25 V), the structural parameters of the porous anodic aluminum oxide template were adjusted. The obtained alumina three-dimensional nano grid structure could be divided into two parts. One part had only longitudinal pores, and the other part contained both longitudinal and lateral pores. These two parts had different effective refractive indices due to different porosities. When light propagated in this structure with periodically alternating refractive indices, interference phenomena occurred due to Bragg reflection, and light with a specific wavelength was reflected, enabling the structure to have the ability of wavelength selection. When the duration of low-voltage oxidation was changed, the length of the part with only longitudinal pores in the structure was modulated. The longer the duration, the longer the distance (t1) between adjacent two lateral pores and the thicker the thickness. This change in the structure caused the porosity of this part to change, affecting the effective refractive index and thus changing the position of the reflection peak.

[0073] When no deionized water was filled, it showed the blue, green, and red colors as shown in Figure 2 (a, c). Among them, when t1 was 270 nm and t2 was 52 nm, it showed blue; when t1 was 300 nm and t2 was 52 nm, it showed green; when t1 was 380 nm and t2 was 52 nm, it showed red.

[0074] When the alumina three-dimensional nano grid structure was filled with deionized water, in-situ dynamic regulation of colors could be achieved, as shown in Figure 2 (b, d). The filling of water would change the effective refractive index of each part, leading to the phenomenon of red shift of the original reflection peak, which was macroscopically manifested as the change of the sample color, as shown in Figure 3The macroscopic color of the sample before and after filling with water changes. Filling 1 mL of water into the sample in this example can achieve complete filling. Figure 2 The water consumption for filling the partial area shown in (d) is 0.5 mL, and the dynamic control of color is achieved by filling water.

[0075] Example 2

[0076] According to Figure 3 the process flow chart shown, prepare the alumina three-dimensional nano-grid structure. The specific steps are as follows:

[0077] Cut the aluminum foil with a purity of 99.95% into aluminum sheets of 5 cm × 7 cm, and sequentially place them in a potassium hydroxide solution with a concentration of 1 M and absolute ethanol for ultrasonic cleaning treatment to obtain pretreated aluminum sheets.

[0078] Immerse the above-mentioned pretreated aluminum sheets into an oxalic acid electrolyte with a concentration of 0.3 M, and perform pulsed anodic oxidation at 15 °C with the aid of a cooling circulating water device. The periodic pulsed voltage applied during the process is specifically a low-voltage oxidation with an applied voltage of 40 V and a duration of 180 s, and a high-voltage oxidation with an applied voltage of 52 V and a duration of 2 s. The two steps of low-voltage oxidation and high-voltage oxidation are alternately carried out for a total of 11 h. Immerse the aluminum sheets that have completed pulsed anodic oxidation into a mixed acidic solution of 1 M copper chloride and 0.1 M hydrochloric acid to remove the remaining unreacted aluminum sheets, and obtain a porous anodic alumina template with a vertical pore structure.

[0079] Immerse the above-mentioned porous anodic alumina template into a phosphoric acid solution with a concentration of 5 wt%, and soak it in a heating environment at 35 °C for 25 min to create nano-lateral pores with a lateral pore spacing of 100 nm and a pore diameter of 50 nm to obtain an alumina matrix. Use a dropper to suck deionized water and drop it onto the surface of the alumina matrix to make the deionized water completely infiltrate, and obtain an alumina three-dimensional nano-grid structure.

[0080] Explore the cooling capacity of the alumina three-dimensional nano-grid structure obtained in Example 2, and build an outdoor radiative cooling performance test device as shown in Figure 4 the figure. This device consists of a computer, a temperature recorder, and a measurement box. The specific design of the measurement box is as shown in Figure 4 b:

[0081] The alumina three-dimensional nanogrid structure obtained in Example 2 was placed in a high-density foam box wrapped with aluminum foil paper to maintain heat insulation and reflect other radiations from the ground. A K-type thermocouple was placed on the back of the sample, and the real-time temperature was tested and recorded by a temperature recorder. Except for the sample area, the top of the measurement box was encapsulated with a heat-reflective aluminized polyethylene terephthalate (PET) film, and the sample area was covered with a polyethylene (PE) film to ensure high transparency to the atmosphere and solar radiation and low non-radiative heat loss. During the outdoor test, the measurement box was exposed to clear conditions. The temperature drop ΔT is represented as the temperature difference (T 环境 -T 样品 ) between this material and the surrounding environment.

[0082] Figure 5 For the infrared spectral changes and the regulation effect of the radiative cooling performance of the alumina three-dimensional nanogrid structure obtained in Example 2 before and after filling with water. Among them, the ambient temperature during the temperature drop test was 27 °C, and the solar irradiance power was 681 W / m 2 ; The temperature drop refers to the temperature difference between this material and the surrounding environment temperature. The specific results are as follows: Before filling with water, a temperature drop of 3.2 °C below the ambient temperature was achieved, and after filling with water, a temperature drop of 2.3 °C below the ambient temperature was achieved, thus realizing the regulation of the refrigeration effect.

[0083] In this example, an alumina three-dimensional nanogrid structure prepared in an oxalic acid electrolyte solution was used. This structure has a unique microscopic morphology, and there are longitudinal and transverse channels inside. These channels endow the material with a unique ability to store and remove liquids. When the three-dimensional channels of alumina are filled with air, strong resonance phenomena will occur in the Al-O bonds inside the material, and then a broadband will be formed in the atmospheric window wavelength region, and a nearly perfect thermal emission effect can be achieved. After adding water to wet it, due to the vibration characteristics of water molecules themselves, the absorption performance of the structure in the infrared band is significantly enhanced, mainly outside the atmospheric window at about 6 μm. This spectral change caused by filling with water directly promotes the increase of thermal emission output and the absorption of atmospheric radiation, and finally affects the overall radiative cooling performance of the structure.

[0084] When the structure is filled with water, its original refrigeration effect changes significantly, which strongly proves that the alumina three-dimensional nanogrid structure obtained in Example 2 has the ability to regulate the radiative cooling performance. In addition, due to the very thin thickness (10 - 200 μm) of the prepared alumina three-dimensional nanogrid structure, it can be quickly dried within a few minutes by blowing, which provides great convenience for its subsequent recycling.

[0085] Example 3

[0086] Prepare the alumina three-dimensional nanogrid structure according to the process flow chart shown in Figure 6 The specific steps are as follows:

[0087] The alumina matrix is prepared according to the method described in Example 2;

[0088] The basic components of PDMS and the curing agent are mixed at a mass ratio of 10:1, and after being fully stirred and mixed, they are left to stand for degassing in a vacuum environment to obtain a PDMS filler;

[0089] The PDMS filler is sucked with a dropper and dropped onto the alumina surface of the alumina matrix, and placed in a vacuum and negative pressure environment to allow the PDMS to fully enter the internal three-dimensional channels, obtaining a PDMS-filled alumina three-dimensional nanogrid structure;

[0090] The alumina three-dimensional nanogrid structure is transferred onto a silicon wafer and placed at room temperature for 24 h until the PDMS is completely cured.

[0091] Figure 7 For the infrared spectrum and radiative cooling performance of the alumina three-dimensional nanogrid structure obtained in Example 3, where the ambient temperature during the temperature drop test is 8 °C and the solar irradiance power is 611 W / m 2 ; It can be seen from Figure 7 the results that there is an absorption peak at 9 μm for the Si-O bond inside the PDMS, which can improve the spectral performance of the AAO itself. The alumina three-dimensional nanogrid structure is placed as a whole in the test device shown in Example 2 Figure 4 and the temperature change on the surface of the alumina three-dimensional nanogrid structure is monitored and recorded in real time with the temperature of the silicon wafer as a control during a specific time period (11:00 - 14:00). As Figure 7 shown, the temperature of the alumina three-dimensional nanogrid structure placed on the silicon wafer is 4.8 - 9.1 °C lower than that of the silicon wafer itself, indicating that this structure has certain radiative cooling performance.

[0092] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on this embodiment without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A three-dimensional alumina nano-grid structure, comprising an alumina matrix having a three-dimensional interconnected pore structure in the transverse and longitudinal directions and a filler filled in the three-dimensional interconnected pore structure in the transverse and longitudinal directions; the color and radiative cooling power are adjusted by storing and removing the filler in the pore structure.

2. The three-dimensional alumina nanogrid structure according to claim 1, wherein The filler is a liquid filler that does not chemically react with the alumina matrix; or a solid polymer filler having an infrared absorption peak chemical bond in the 8-13 μm band.

3. The three-dimensional alumina nanogrid structure according to claim 2, characterized in that, The liquid filler includes one or more of water, alcohol reagents, and ketone reagents; The solid polymer filler includes one or more of polydimethylsiloxane, polymethyl methacrylate, polyvinyl chloride, and polyphenylene ether resin.

4. The three-dimensional alumina nanogrid structure according to claim 1, wherein, The pore spacing of the transverse pores of the three-dimensional alumina nano-grid structure is 150-620 nm, and the pore spacing of the longitudinal pores is 30-600 nm; the pore diameter of the transverse pores is 35-60 nm, and the pore diameter of the longitudinal pores is 40-200 nm.

5. The preparation method of the alumina three-dimensional nano-grid structure according to any one of claims 1 to 4, characterized in that, It includes the following steps: Subject the aluminum material to pulsed anodic oxidation to obtain a porous anodic alumina template with vertical pores; Perform transverse acid etching on the porous anodic alumina template to obtain an alumina matrix with transverse and vertical pores; Fill the pore structure of the alumina matrix to obtain the three-dimensional alumina nano-grid structure.

6. The preparation method according to claim 5, characterized in that, The electrolyte for the pulsed anodic oxidation is a polyacid electrolyte.

7. The preparation method according to claim 6, characterized in that, The voltage of the pulsed anodic oxidation consists of an alternating low-field voltage and high-field voltage; When the polyacid electrolyte is a sulfuric acid solution, the low-field voltage is 20-27 V, and the duration is 100-530 s; the high-field voltage is 32-40 V, and the duration is 2-5 s; When the polyacid electrolyte is an oxalic acid solution, the low-field voltage is 40-47 V, and the duration is 100-530 s; the high-field voltage is 52-60 V, and the duration is 2-5 s; When the polyacid electrolyte is a phosphoric acid solution, the low-field voltage is 195-202 V, and the duration is 100-530 s; the high-field voltage is 255-263 V, and the duration is 2-5 s; The total time of the pulsed anodic oxidation is 2-36 h, and the temperature is 5-25 °C.

8. The preparation method according to claim 6, characterized in that, The concentration of the polyacid electrolyte is 0.2-0.8 M.

9. The preparation method according to claim 4, characterized in that, The reagent used for the acid etching is a phosphoric acid solution with a concentration of 5-8 wt%; The temperature of the acid etching is 30-60 °C, and the time is 10-40 min.

10. The application of the three-dimensional alumina nano-grid structure according to any one of claims 1-4 or the three-dimensional alumina nano-grid structure prepared by the preparation method according to any one of claims 5-9 in a building, vehicle, or clothing with a radiative cooling function.

Images