Self-cleaning dual-mode aerogel film as well as preparation method and application thereof

Abstract

The invention relates to a self-cleaning dual-mode aerogel film and a preparation method and application thereof.The preparation method comprises the following steps that original protein fibers are pretreated, and pretreated protein fibers are obtained; mixing the pretreated protein fibers with water to form a suspension A, adding a cross-linking agent into the suspension A to obtain a suspension B, and freeze-drying the suspension B to obtain blank aerogel; spraying a composite solution containing a mixed adhesive and light absorption particles on the surface of one side of the blank aerogel, and drying to obtain mixed aerogel; and spraying hydrophobic modifiers on the surfaces of the two sides of the mixed aerogel, and drying to obtain the self-cleaning dual-mode aerogel film. According to the invention, protein fibers are used as a main raw material to prepare blank aerogel, a composite solution is sprayed on the blank aerogel, a heating surface is formed through the photothermal conversion performance of light-absorbing particles, the other side is a cooling surface, intelligent response to refrigeration or heating requirements is realized, and the aerogel film has a self-cleaning capability through hydrophobic modification.

Description

Technical Field

[0001] The invention relates to the field of functional membrane materials, and in particular to a self-cleaning dual-mode aerogel film and a preparation method and application thereof. Background Art

[0002] As global energy consumption increases and climate change intensifies, finding energy-efficient cooling solutions becomes increasingly important. Radiative cooling technology, as an emerging passive cooling method, has attracted widespread attention due to its potential to reduce the temperature of objects without external energy input. Radiative cooling is based on the principle that objects dissipate heat energy into the cold outer space through infrared radiation. This heat dissipation process mainly occurs in the atmospheric window, that is, the infrared band with a wavelength range of approximately 8-13 microns. Radiation in this band can penetrate the atmosphere and effectively transfer heat to outer space.

[0003] Radiative cooling technology can be widely used in building energy conservation, fresh water collection, electronic equipment heat dissipation, intelligent temperature control systems and other fields, demonstrating its potential in promoting energy efficiency and addressing climate change. Most of the radiative cooling functional materials focus on the design of photonic crystal structures, such as photonic crystal materials, multilayer structures and micro-nano porous structure materials.

[0004] However, there is little research on dual-mode, self-cleaning materials with radiative cooling and solar heating performance, resulting in the existing radiative cooling functional materials having relatively simple performance and being unable to achieve dual-mode regulation of cooling and heating. In addition, pollutants such as dust are easily deposited on the surface, resulting in a decrease in radiation performance. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned technical deficiencies, provide a self-cleaning dual-mode aerogel film and its preparation method and application, and solve the technical problem that the performance of the radiation refrigeration functional material in the prior art is relatively single and the dual-mode adjustment of cooling and heating cannot be achieved.

[0006] In order to achieve the above technical purpose, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for preparing a self-cleaning dual-mode aerogel film, comprising the following steps: S1, pre-treating raw protein fibers to obtain pre-treated protein fibers; S2, mixing the pre-treated protein fibers with water to form a suspension A, adding a cross-linking agent to the suspension A to obtain a suspension B, and freeze-drying the suspension B to obtain a blank aerogel; S3, spraying a composite solution containing a mixed adhesive and light-absorbing particles on one surface of the blank aerogel, and drying to obtain a mixed aerogel; S4, spraying a hydrophobic modifier on both sides of the mixed aerogel, and drying to obtain a self-cleaning dual-mode aerogel film.

[0007] In a second aspect, the present invention provides a dual-mode aerogel film prepared by the above preparation method.

[0008] In a third aspect, the present invention provides an application of a dual-mode aerogel film as a radiation cooling functional material, a photothermal conversion material and / or a thermal insulation material.

[0009] Compared with the prior art, the beneficial effects of the present invention include: The present invention uses protein fiber as the main raw material to prepare blank aerogel, sprays a composite solution containing a mixed adhesive and light-absorbing particles on the blank aerogel, forms a heating surface through the light-heat conversion performance of the light-absorbing particles, and the other side is a cooling surface, which has high reflectivity to sunlight, thereby realizing intelligent response to refrigeration or heating needs; and after hydrophobic modification, the aerogel film has good self-cleaning ability, improves film performance, and is conducive to extending service life. The aerogel film of the present invention can realize dual-mode regulation of energy-free radiation cooling and solar heating, which not only helps to improve the performance and application scope of radiation refrigeration technology, but also has important significance for promoting energy efficiency and responding to climate change. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A diagram of a refrigeration test device for the radiation refrigeration film of the present invention; Figure 2 The surface microscopic morphology of the self-cleaning blank aerogel radiation cooling film in Comparative Example 1 of the present invention, (a) scale 500um, (b) scale 200um, (c) scale 20um; Figure 3 The surface microscopic morphology of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 of the present invention, (a) scale 500um, (b) scale 200um, (c) scale 20um; Figure 4 The self-cleaning performance test process of the heating surface of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 of the present invention is shown in Figure 1. (a) is an optical photograph of the film when a colored dye is dropped on the surface when the film is laid flat, and (a1), (a2), and (a3) ​​are optical photographs before, during, and after self-cleaning, respectively. Figure 5 1 is a process diagram of the self-cleaning performance test of the cooling surface of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 of the present invention, (b) is an optical photograph of the film when a colored dye is dropped on the surface when the film is laid flat, (b1) (b2) and (b3) are optical photographs before, during and after self-cleaning, respectively.

[0011] Figure 6 This is a heating performance effect diagram of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 of the present invention and the self-cleaning blank aerogel radiative cooling film prepared in Comparative Example 1; Figure 7 This is a diagram showing the cooling effect of outdoor testing of the cooling surface of 10 multi-walled carbon nanotube / silk fiber aerogel films in Example 4 of the present invention; Figure 8 This is an infrared emissivity diagram of the self-cleaning blank aerogel radiation cooling film in Comparative Example 1 of the present invention; Fig. 9 These are optical photographs of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 of the present invention and the aerogel film made in Comparative Example 2, wherein (a) is Example 4 and (b) is Comparative Example 2.

[0012] Fig.10 Schematic diagram of contact angles of the bottom and top surfaces (before and after hydrophobic modification) of Example 4 and Comparative Example 3 of the present invention, wherein (a) (b) are Comparative Example 3 (before hydrophobic modification), and (a1) (b1) are Example 4 (after hydrophobic modification). DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0014] At present, most of the radiation cooling functional materials are concentrated on the design of photonic crystal structures, such as photonic crystal materials, multilayer structures and micro-nano porous structure materials, which usually have high requirements for raw materials, resulting in high costs; and traditional technologies have less research on dual-mode and self-cleaning performance materials of radiation cooling and solar heating, resulting in the existing radiation cooling functional materials with relatively single performance, unable to achieve dual-mode adjustment of cooling and heating, and pollutants such as dust are easily deposited on the surface, resulting in a decrease in radiation performance.

[0015] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a self-cleaning dual-mode aerogel film and its preparation method and application, using protein fiber as the main raw material, combined with other materials, to develop a protein fiber material that can adjust the thermal radiation performance according to changes in environmental conditions, so as to achieve intelligent response to cooling or heating needs. The aerogel film of the present invention can achieve dual-mode adjustment of energy-free radiation cooling and solar heating, which not only helps to improve the performance and application scope of radiation refrigeration technology, but also has important significance for promoting energy efficiency and responding to climate change.

[0016] In a first aspect, the present invention provides a method for preparing a self-cleaning dual-mode aerogel film, comprising the following steps: S1, pretreating the original protein fiber to obtain pretreated protein fiber; S2, mixing the pretreated protein fibers with water to form a suspension A, adding a cross-linking agent to the suspension A to obtain a suspension B, and freeze-drying the suspension B to obtain a blank aerogel; S3, spraying a composite solution containing a mixed adhesive and light-absorbing particles on one surface of a blank aerogel, and drying to obtain a mixed aerogel; S4, spraying a hydrophobic modifier on both sides of the hybrid aerogel surface, and drying to obtain a self-cleaning dual-mode aerogel film.

[0017] Preferably, in step S1, the pretreatment is to immerse the raw protein fibers in a first organic solvent, then wash them in deionized water and dry them. By pretreating the raw protein fibers, the hydrogen bond network between the fiber chains can be destroyed, so as to reduce the energy consumption of producing nanofibers, and facilitate the subsequent acquisition of nanofibers with uniform size and good dispersion.

[0018] Further preferably, the first organic solvent includes ethanol, propanol, isopropanol or acetone; the dosage relationship between the original protein fiber and the first organic solvent is 1 g: (30-60) mL, more preferably 1 g: 50 mL; the drying conditions are: drying temperature 50-60°C, drying time 6-10h.

[0019] Preferably, in step S1, the raw protein fiber includes one or more of pig hair fiber, silk fiber, sheep wool fiber and rabbit hair fiber.

[0020] More preferably, the original protein fiber is original silk protein fiber. The present invention uses silk protein fiber as the main raw material, wherein the silk protein fiber is derived from nature, has good mechanical properties, biocompatibility, biodegradability and excellent thermal properties, and by combining the silk protein fiber with other materials, it is more conducive to the development of silk protein fiber materials that can adjust the thermal radiation performance according to changes in environmental conditions, and better realize the intelligent response to the demand for cooling or heating.

[0021] Preferably, in step S2, the suspension A is pre-treated protein fiber mixed with water and then heated at 30000-36000 r·min -1 In the present invention, the pretreated protein fibers are broken up by a high-speed rotation of a stirrer to obtain nanofibers.

[0022] Preferably, in step S2, in the suspension A, the ratio between the pretreated protein fiber and water is (0.3-0.5) g:100 mL; more preferably 0.4 g:100 mL.

[0023] Preferably, in step S2, the cross-linking agent includes one or more of polyvinyl alcohol, glyoxal, polyethylene glycol and glycerol; preferably polyvinyl alcohol.

[0024] Preferably, in step S2, the amount of the cross-linking agent used is 0.3% to 0.5% of the mass of the pretreated protein fiber, and more preferably 0.5%.

[0025] Preferably, in step S2, after adding the cross-linking agent to the suspension A, the suspension is stirred and ultrasonicated for 20 to 40 minutes to allow the polyvinyl alcohol to fully react with the pretreated protein fibers.

[0026] Preferably, in step S2, freeze drying is performed by precooling at -40 to -60°C for 24 to 48 hours, freezing at -160 to -200°C in liquid nitrogen for 10 to 40 minutes, and finally freeze drying at -70 to -90°C in a vacuum freeze-drying process for 40 to 50 hours.

[0027] Preferably, in step S3, the composite solution containing the mixed adhesive and the light absorbing particles is obtained by dissolving the mixed adhesive and the light absorbing particles in a second organic solvent; The mixed adhesive is a mixed solution of polyvinyl alcohol aqueous solution and 3-aminopropyltriethoxysilane in a volume ratio of 3:2, and the concentration of the polyvinyl alcohol aqueous solution is 0.01-0.03 g / mL; The volume ratio of the mixed adhesive to the second organic solvent is 1:(5-10); more preferably 1:8; The light-absorbing particles include one or more of carbon black, graphene, multi-walled carbon nanotubes, carbon nanotubes and graphite; more preferably, multi-walled carbon nanotubes; The ratio of the light absorbing particles to the second organic solvent is (0.8-1.2) g:500 mL; The second organic solvent includes one or more of ethanol, acetone and methanol.

[0028] More preferably, the particle size of the light absorbing particles is 450 to 550 nm, more preferably 500 nm±10 nm.

[0029] Preferably, in step S3, the spraying process conditions of the composite solution are: spraying distance is 4-6 cm, spraying time is 5s-15s, and nozzle pressure is 0.2-0.4Mpa; more preferably, the spraying time is 10s and the nozzle pressure is 0.3Mpa.

[0030] Preferably, in step S3, the drying temperature is 40-60° C. and the drying time is 5-10 hours.

[0031] Preferably, in step S4, the spraying process conditions of the hydrophobic modifier are: spraying distance is 4-6 cm, spraying time is 1-3 s, and nozzle pressure is 0.2-0.4 Mpa; more preferably, the spraying distance is 5 cm, the spraying time is 2 s, and the nozzle pressure is 0.3 Mpa.

[0032] Preferably, in step S4, the hydrophobic modifier includes one or more of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, perfluorobutyltriethoxysilane, perfluorooctyltriethoxysilane and perfluorodecyltrimethoxysilane; more preferably 1H,1H,2H,2H-perfluorooctyltrimethoxysilane.

[0033] Preferably, in step S4, the drying temperature is 40-60° C., and the drying time is 2-5 hours.

[0034] In a second aspect, the present invention provides a dual-mode aerogel film prepared by the above preparation method.

[0035] In a third aspect, the present invention provides an application of a dual-mode aerogel film as a radiation cooling functional material, a photothermal conversion material and / or a thermal insulation material.

[0036] The mechanism of action and advantages of the present invention are: (1) The present invention utilizes protein fibers from sustainable sources in nature as the basic material, which has the advantages of low cost, biodegradability, green renewableness, and environmental protection. In addition, its good softness, hygroscopicity, comfort, and breathability give it additional functions, which is of great significance in expanding the effective utilization of biomass materials.

[0037] (2) The present application sprays a composite solution on one side of a blank aerogel through the coordination of various materials to form a heating surface, and the other side is a cooling surface; wherein the cooling surface can achieve a good radiation cooling effect, which not only saves costs, but also has a good self-cleaning property after hydrophobic modification, avoids the deposition of pollutants on the surface, improves the radiation cooling and solar heating effects, and has a long service life; and compared with other radiation cooling films, the dual-mode film with self-cleaning ability prepared by the present invention can simultaneously achieve energy-free radiation cooling and solar heating through the difference in material composition on both sides, wherein the cooling effect of the cooling surface is derived from the rich CO functional groups in the protein fiber, which has a strong infrared absorption peak in the fingerprint area, and its atmospheric transparent window reflects a high emissivity and high porosity structure, thereby increasing diffuse reflection and achieving high reflection of sunlight, allowing the film to cool objects in hot summer; and the heating effect of the heating surface is mainly derived from the photothermal conversion performance of the light-absorbing particles, allowing the film to heat objects in cold winter.

[0038] (3) The self-cleaning dual-mode film prepared by the present invention can be used for the preparation of energy-free radiation cooling and solar heating aerogel films. Its integrated design provides a way to achieve synergistic multifunctionality, which will release huge potential in sustainable cooling and heating.

[0039] (4) The preparation method of the present invention has simple process, convenient operation, high production efficiency, low cost and energy consumption. The prepared dual-mode film with self-cleaning has good self-cleaning properties and has great application prospects.

[0040] The present invention is further described in detail below through specific embodiments and comparative examples; in the following embodiments and comparative examples, the raw material silk fiber used comes from: Hebei Runfeng Textile Co., Ltd.; the light-absorbing particles of carbon black, graphene, multi-walled carbon nanotubes, carbon nanotubes or graphite used are all purchased from Aladdin Company, and the average particle size is 500±10 nm.

[0041] Example 1 S1, the original silk protein fiber was immersed in ethanol at a ratio of 1 g:50 mL for 6 h, then ultrasonically cleaned in deionized water at a ratio of 1 g:50 mL for 30 min, and dried at 60 °C for 7 h to obtain the pretreated silk protein fiber.

[0042] S2, 0.4 g of pretreated silk protein fibers were dispersed in 100 mL of deionized water and heated at 35000 r·min -1 The suspension A was prepared by mechanically breaking at a speed of 1000 rpm, and then polyvinyl alcohol (Da: 1750) was added to the suspension A, and the amount of polyvinyl alcohol was 0.5% of the mass of the pretreated silk protein fiber. The suspension was stirred and ultrasonicated for 30 minutes to obtain the suspension B. The suspension B was poured into a cylindrical mold with a thickness of 0.5 cm and a diameter of 6 cm and pre-frozen at a temperature of -50°C for 24 hours; then frozen with liquid nitrogen at a temperature of -180°C for 30 minutes; and then vacuum freeze-dried (cold trap temperature of -80°C) for 48 hours to obtain a blank aerogel.

[0043] S3, dissolving a mixed adhesive (0.02 g / mL polyvinyl alcohol aqueous solution and 3-aminopropyltriethoxysilane, with a volume ratio of 3:2) and light-absorbing particle carbon black in ethanol to prepare a composite solution, wherein the volume ratio of the mixed adhesive to ethanol is 1 mL:8 mL, and the amount of carbon black to ethanol is 1 g:500 mL.

[0044] The composite solution was sprayed on the bottom surface of the blank aerogel at a spraying distance of 5 cm, a spraying time of 5 s, a nozzle pressure of 0.3 MPa, and dried at 50°C for 7 h to form a heating surface to obtain a mixed aerogel.

[0045] S4, spray 1H,1H,2H,2H-perfluorooctyltrimethoxysilane hydrophobic modifier on the bottom and top surfaces of the obtained mixed aerogel, the spraying distance is 5 cm, the spraying time is 2 s, the nozzle pressure is 0.3 MPa, and the mixture is dried at 50 °C for 4 h to obtain a self-cleaning dual-mode film integrating radiative cooling and solar heating, which is recorded as 5 carbon black / silk fiber aerogel film.

[0046] Example 2 The only difference between this embodiment and embodiment 1 is that the added light absorbing particles are multi-walled carbon nanotubes, and the other steps and conditions are the same as those in embodiment 1. The obtained self-cleaning dual-mode film integrating radiative cooling and solar heating is recorded as 5 multi-walled carbon nanotube / silk fiber aerogel film.

[0047] Example 3 The only difference between this embodiment and embodiment 1 is that the raw fibers used are sheep wool fibers, and the other steps and conditions are the same as those in embodiment 1. The obtained self-cleaning dual-mode film integrating radiative cooling and solar heating is recorded as 5 carbon black / sheep wool fiber aerogel film.

[0048] Example 4 The only difference between this embodiment and embodiment 2 is that the spraying time is 10 seconds, and the other steps and conditions are the same as those of embodiment 2. The obtained self-cleaning dual-mode film integrating radiative cooling and solar heating is recorded as 10 multi-walled carbon nanotube / silk fiber aerogel film.

[0049] Comparative Example 1 The only difference from Example 4 is that no light absorbing particles are added when preparing the composite solution; the other steps and conditions are the same as those of Example 4. A self-cleaning blank aerogel radiation cooling film is prepared.

[0050] The results showed that the aerogel obtained after spraying the composite solution without adding light-absorbing particles is only suitable for high temperature environments in summer, and cannot provide heating performance in cold winter, and cannot achieve the integration of heating and cooling performance.

[0051] Comparative Example 2 The only difference from Example 4 is that no mixed adhesive is added when preparing the composite solution; the other steps and conditions are the same as those of Example 4.

[0052] The results showed that the multi-walled carbon nanotubes without mixed adhesive had low adhesion to the bottom surface of the aerogel and were easy to fall off.

[0053] Comparative Example 3 The only difference from Example 4 is that the bottom and top surfaces of the prepared hybrid aerogel are not sprayed with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane hydrophobic modifier, and the other steps and conditions are the same as those in Example 4.

[0054] The results showed that the aerogel film without the hydrophobic modifier was highly hydrophilic and had no self-cleaning properties. Figure 3 Self-cleaning process diagram and Fig. 9This is also proved by the contact angle test diagrams of the bottom surface (a, a1) and the top surface (b, b1) before and after hydrophobic modification. 1H, 1H, 2H, 2H-perfluorooctyl trimethoxysilane has low surface energy and low polarity of fluorinated alkyl chains; it can also form covalent bonds with the surface of inorganic materials to fix the fluorinated alkyl chains on the surface of the material, thereby providing lasting hydrophobicity. In addition, the bond energy between fluorine atoms and carbon atoms is large, making it difficult for fluorinated alkyl chains to form hydrogen bonds with water molecules, providing conditions for the hydrophobicity of aerogels.

[0055] Example 5 The only difference from Example 4 is that the bottom and top surfaces of the prepared mixed aerogel are sprayed with one of the hydrophobic modifiers, namely perfluorobutyltriethoxysilane, perfluorooctyltriethoxysilane or perfluorodecyltrimethoxysilane, and the other steps and conditions are the same as those in Example 4.

[0056] The results showed that when spraying perfluorobutyltriethoxysilane, the water contact angles of the heating surface and the cooling surface were 135.2° and 120.3° respectively; when spraying perfluorooctyltriethoxysilane, the water contact angles of the heating surface and the cooling surface were 138.4° and 126.5° respectively; when spraying perfluorodecyltrimethoxysilane, the water contact angles of the heating surface and the cooling surface were 140.6° and 129.8° respectively; and when spraying H,1H,2H,2H-perfluorooctyltrimethoxysilane, the water contact angles of the heating surface and the cooling surface were 145.6° and 134.6° respectively, which have better hydrophobicity and can better meet the outdoor application of aerogel.

[0057] Performance Testing 1. Test method or instrument description: (1) Infrared emissivity test: The infrared emissivity test standard of aerogel film is based on JJF (Textile) 086-2019.

[0058] (2) Surface morphology detection of radiation cooling film: characterization was performed using a scanning electron microscope (JSM-6510).

[0059] (3) Static water contact angle test: Use a contact angle meter (JC2000C2E) to measure the contact angle of the sample.

[0060] (4) Outdoor test of cooling performance of cooling surface of radiant cooling film: The cooling test device of radiant cooling film is shown in Figure 1; It is a foam box with a size of 80cm×40cm×30cm. A plurality of grooves with a diameter of 3cm and a depth of 1cm are set on the foam board on the top surface of the foam box. The film to be tested (a disc with a diameter of about 3cm) is placed in the groove, and a layer of polyethylene film is covered on the upper surface of the film to be tested to shield the influence of thermal convection. The lower surface of the film to be tested is connected to a K-type thermocouple to test the temperature of the surface of the film to be tested. A four-channel temperature recorder (TA612C) is used to record the real-time temperature. The entire foam box is wrapped with tin foil to shield the surrounding radiation. The polyethylene film is used as a blank control, and the lower surface of the polyethylene film is connected to a K-type thermocouple to test the temperature of the polyethylene film and the air surface. A solar photometer (TES-132) is used to measure the solar power.

[0061] (5) Indoor performance test of the heating surface of the radiant cooling film: at 900 W / m 2 In an indoor xenon lamp to simulate a cold environment (5°C), the film was prepared into a cylinder with a diameter of 3 cm and a thickness of 6 mm and placed 25 cm away from the xenon lamp. The lower surface of the film to be tested was connected to a K-type thermocouple to test the temperature of the bottom surface of the film to be tested. A four-channel temperature recorder (TA612C) was used to record the real-time temperature.

[0062] 2. Test results: Figure 2 The surface micromorphology of the self-cleaning blank aerogel radiative cooling film in comparative example 1 is shown. (a), (b) and (c) are the surface micromorphologies of the self-cleaning blank aerogel radiative cooling film in comparative example 1 with a scale of 500 um, 200 um and 20 um, respectively. It can be seen that the film surface is a rough multi-level porous structure, which enhances the reflectivity of the film in the visible light / near infrared band and the emissivity in the 8-13 μm band; at the same time, this provides conditions for the low thermal conductivity of the sample.

[0063] Figure 3 The surface micromorphology of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 is shown. (a), (b) and (c) are the surface micromorphologies of the 10 multi-walled carbon nanotube / silk fiber aerogel films with a scale of 500 um, 200 um and 20 um, respectively. It can be seen that the surface of the film is evenly covered with a layer of multi-walled carbon nanotubes, which provides conditions for the light-heat conversion of the film, so that the film can achieve heating performance in the cold winter.

[0064] Figure 4The self-cleaning performance characterization of the heating surface of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 is demonstrated. (a) shows an optical photograph of various dyes in a spherical shape on the heating surface of the aerogel, reflecting its excellent hydrophobic properties. (a1) (a2) (a3) ​​respectively show optical photographs before, during and after self-cleaning. First, the aerogel film prepared in Example 4 is cut into films with a size of 20mm×50mm, and then the cut films are placed on a clean quartz glass sheet (20mm×70mm) tilted in a culture dish, and soil is placed on top of the samples; then water is dripped on the sample with a dropper, and it can be seen that the soil on the surface of the sample will slide off the surface of the sample with the water droplets; as all the soil slides off, the membrane achieves surface self-cleaning, and the surface is as smooth as before.

[0065] Figure 5 The self-cleaning performance characterization of the cooling surface of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 is demonstrated. (b) shows an optical photograph of various dyes in a spherical shape on the heating surface of the aerogel, reflecting its excellent hydrophobic properties. (b1) (b2) (b3) respectively show optical photographs before, during and after self-cleaning. First, the aerogel film prepared in Example 4 is cut into films with a size of 20mm×50mm, and then the cut films are placed on a tilted clean quartz glass sheet (20mm×70mm) in a culture dish, and soil is placed on top of the samples; then water is dripped on the sample with a dropper, and it can be seen that the soil on the surface of the sample will slide off the surface of the sample with the water droplets; as all the soil slides off, the membrane achieves surface self-cleaning and the surface is as smooth as before.

[0066] Figure 6 The 10 multi-walled carbon nanotube / silk fiber aerogel films (MWCNTs@SNF b ) and the heating performance effect diagram of the self-cleaning blank aerogel radiative cooling film (SNF aerogel) prepared in Example 1. Simulating a cold environment (5°C), at 900 W / m 2 Under an indoor xenon lamp, at a distance of 25 cm from the xenon lamp, the aerogel films of Example 4 and Comparative Example 1 were respectively prepared into cylinders with a diameter of 3 cm and a thickness of 6 mm. The data showed that Example 4 and Comparative Example 1 could achieve an average heating effect of 75°C and 45°C respectively compared with the ambient temperature, indicating that Example 4 has a better heating effect.

[0067] Figure 7The cooling effect of the outdoor test of the 10 multi-walled carbon nanotube / silk fiber aerogel film cooling surface in Example 4 is shown, and the polyethylene film (PE film) and silk fabric covering are used as two control groups. When the outdoor ambient temperature is 16℃-32℃, the sample is made into a cylinder with a diameter of 3cm and a thickness of 6mm. The data shows that compared with the polyethylene film (PE film) covering, the aerogel film cooling surface of the present invention can achieve a cooling effect of 14.1℃, and has an average cooling effect of 5.1℃ more than the silk fabric.

[0068] The aerogel films of the above embodiments and comparative examples are statistically tested at a solar power of 950-1050 W / m 2 The average cooling effect of the outdoor test cooling surface at 900 W / m 2 The average temperature rise effect that can be achieved by the heating surface under the indoor xenon lamp is compared with the self-cleaning blank aerogel radiation cooling film in Comparative Example 1. The results are shown in Table 1 below.

[0069] Table 1 Cooling effect of cooling surface and relative average heating effect of heating surface in each embodiment

[0070] As shown in Table 1, the aerogel film prepared in the embodiment of the present invention has a high thermal conductivity when the solar power is 950-1050 W / m 2 In outdoor tests, the cooling surface can achieve an average cooling effect of 8 to 11°C; at 900 W / m 2 Compared with the self-cleaning blank aerogel radiation cooling film in Comparative Example 1, the heating surface under the indoor xenon lamp can achieve an average heating effect of 40 to 75°C.

[0071] Figure 8 The infrared emissivity graph of the self-cleaning blank aerogel radiative cooling film in Comparative Example 1 (the cooling surface of the 10 multi-walled carbon nanotube / silk fiber aerogel film in Example 4 is the same) is shown. The data show that the average emissivity of the aerogel film (i.e., the cooling surface of the aerogel film of the present invention) within the atmospheric window range is 85.1%, and the maximum emissivity is 92.9%, which has good radiative cooling performance.

[0072] Fig. 9In the figure, (a) shows an optical photograph of the aerogel film prepared in Example 4, and (b) shows an optical photograph of the aerogel film prepared in Comparative Example 2. In comparative example 2, the multi-walled carbon nanotubes without the addition of the mixed adhesive have low adhesion to the bottom surface of the aerogel film, and the multi-walled carbon nanotube coating is very easy to fall off in water, and as the coating falls off, the hydrophobicity of the aerogel film is correspondingly reduced; while in Example 4, the multi-walled carbon nanotubes have high adhesion to the bottom surface of the aerogel film, which is mainly due to the formation of hydrogen bonds between the amino groups in 3-aminopropyltriethoxysilane and the oxygen atoms on the surface of the multi-walled carbon nanotubes. The ethoxy part in 3-aminopropyltriethoxysilane interacts with the hydrophobic surface of the multi-walled carbon nanotubes. In addition, its silanol group forms a covalent bond with the oxygen atoms on the surface of the multi-walled carbon nanotubes, thereby improving the interfacial compatibility of the multi-walled carbon nanotubes with other materials and enhancing the compatibility of the composite material. The hydroxyl groups in the polyvinyl alcohol molecules can form hydrogen bonds with the oxygen functional groups (such as carboxyl, hydroxyl or epoxy) on the surface of the multi-walled carbon nanotubes, which helps the two to form a stable dispersion system. Through the cooperation of the mixed adhesive, the adhesion of the light-absorbing particles and the aerogel substrate is synergistically enhanced.

[0073] Fig.10 In the figure, (a) and (b) respectively show the contact angles of the bottom and top surfaces of the aerogel film in comparative example 3 after contact with water droplets at 1s, 2s, and 3s, and (a1) and (b1) respectively show the contact angles of the bottom and top surfaces of the aerogel film in example 4 after contact with water droplets at 1s, 2s, and 3s. The results show that after spraying the hydrophobic modifier 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane, the contact angles of the bottom and top surfaces of the aerogel film in example 4 are significantly improved, showing good water resistance, achieving a self-cleaning effect, and being suitable for outdoor use of the film.

[0074] Therefore, the series of self-cleaning dual-mode films prepared by the present invention not only have self-cleaning properties but also realize radiative cooling in hot summer and heating in cold winter, can realize energy-free radiative cooling and solar heating, and can be used as radiative refrigeration functional materials, photothermal conversion materials, and thermal insulation materials, etc., which help to meet application needs in changes in outdoor environments.

[0075] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a self-cleaning dual-mode aerogel film, characterized in that: The following steps are involved: S1, pretreating the original protein fiber to obtain pretreated protein fiber; S2, mixing the pretreated protein fibers with water to form a suspension A, adding a cross-linking agent to the suspension A to obtain a suspension B, and freeze-drying the suspension B to obtain a blank aerogel; S3, spraying a composite solution containing a mixed adhesive and light-absorbing particles on one surface of a blank aerogel, and drying to obtain a mixed aerogel; S4, spraying a hydrophobic modifier on both sides of the hybrid aerogel surface, and drying to obtain a self-cleaning dual-mode aerogel film.

2. The method for preparing a self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S1, the pretreatment is to immerse the original protein fiber in a first organic solvent, then wash it in deionized water and dry it; The first organic solvent includes ethanol, propanol, isopropanol or acetone; Drying conditions are: drying temperature 50-60°C, drying time 6-10h; The raw protein fiber includes one or more of pig hair fiber, silk fiber, sheep wool fiber and rabbit hair fiber.

3. The method for preparing the self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S2, the suspension A is a mixture of pre-treated protein fibers and water and then heated at 30,000 to 36,000 r / min. -1 The rotation speed is mechanically broken into pieces; In the suspension A, the ratio between the pretreated protein fiber and water is (0.3-0.5) g:100 mL; The cross-linking agent includes one or more of polyvinyl alcohol, glyoxal, polyethylene glycol and glycerol; The amount of the cross-linking agent used is 0.3% to 0.5% of the mass of the pretreated protein fiber.

4. The method for preparing a self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S2, the freeze drying is first pre-cooled at -40 to -60°C for 24 to 48 hours, then frozen in liquid nitrogen at -160 to -200°C for 10 to 40 minutes, and finally freeze-dried in a vacuum at -70 to -90°C for 40 to 50 hours.

5. The method for preparing a self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S3, the composite solution containing the mixed adhesive and the light absorbing particles is obtained by dissolving the mixed adhesive and the light absorbing particles in a second organic solvent; The mixed adhesive is a mixed solution of polyvinyl alcohol aqueous solution and 3-aminopropyltriethoxysilane in a volume ratio of 3:2, and the concentration of the polyvinyl alcohol aqueous solution is 0.01-0.03 g / mL; The volume ratio of the mixed adhesive to the second organic solvent is 1:(5-10); The light absorbing particles include one or more of carbon black, graphene, multi-walled carbon nanotubes, carbon nanotubes and graphite; The ratio of the light absorbing particles to the second organic solvent is (0.8-1.2) g:500 mL; The second organic solvent includes one or more of ethanol, acetone and methanol.

6. The method for preparing a self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S3, the spraying process conditions of the composite solution are: spraying distance is 4-6 cm, spraying time is 5s-15s, and nozzle pressure is 0.2-0.4Mpa.

7. The method for preparing a self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S4, the spraying process conditions of the hydrophobic modifier are: spraying distance is 4 to 6 cm, spraying time is 1 to 3 s, and nozzle pressure is 0.2 to 0.4 MPa.

8. The method for preparing a self-cleaning dual-mode aerogel film according to claim 1, characterized in that: In step S4, the hydrophobic modifier includes one or more of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, perfluorobutyltriethoxysilane, perfluorooctyltriethoxysilane and perfluorodecyltrimethoxysilane.

9. A self-cleaning dual-mode aerogel film prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the dual-mode aerogel film according to claim 9 as a radiation cooling functional material, a photothermal conversion material and / or a thermal insulation material.

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