Preparation method of a radiation cooling film based on metal organic framework UIO-66

Abstract

The application relates to a preparation method of a radiation refrigeration film based on a metal organic framework UIO-66, and relates to a preparation method of a radiation refrigeration film. The purpose of the application is to solve the problems of great technical difficulty, high cost, poor radiation refrigeration performance and difficult realization of scale popularization and application of a radiation refrigeration material. The method comprises the following steps: I, preparing a surface-modified metal organic framework UIO-66; II, preparing a PDMS solution; III, adding the surface-modified metal organic framework UIO-66 into the PDMS solution, stirring uniformly, then adding a curing agent of the PDMS, stirring and mixing, then pouring, curing into a film, peeling and obtaining the radiation refrigeration film based on the metal organic framework UIO-66. The application has the advantages of simple preparation process, low cost and remarkable refrigeration effect. The application can obtain the radiation refrigeration film based on the metal organic framework UIO-66.

Description

Technical Field

[0001] This invention relates to a method for preparing a radiation-cooled thin film. Background Technology

[0002] As global warming intensifies, people are forced to rely on active cooling methods such as air conditioning to achieve comfortable ambient temperatures. However, these traditional electric cooling technologies consume significant amounts of energy and emit greenhouse gases, hindering efforts to address energy depletion and global warming. Therefore, there is a need to develop energy-efficient and environmentally friendly cooling methods. Radiative cooling, a passive cooling technology that requires no electricity input, is becoming an attractive cooling strategy. Radiative cooling technology works by reflecting most of the sunlight (0.3-2.5μm) and transferring excess heat through atmospheric windows as infrared radiation to the cold outer space (≈3K), making it a zero-consumption, zero-pollution cooling technology.

[0003] Among various materials for achieving radiative cooling, polymer-based radiative cooling materials have attracted widespread attention due to their inherent high emissivity in the mid-infrared band and ease of large-scale processing and application. Patent document CN 111393915 A discloses a passive radiative cooling composite material layer. This layer uses functional inorganic nanoparticles such as Al2O3 and SiO2 to reflect sunlight, functional polymers such as cellulose acetate and polyvinylidene fluoride to enhance radiation, and resins such as epoxy resin and polyurethane resin to improve coating adhesion. This composite material layer is simple to prepare, easy to operate, and can be applied in multiple fields such as textiles and construction. Patent document CN 110372976 B discloses a reflective radiative cooling material, comprising a polymer substrate and ceramic particles dispersed within the polymer substrate. This material can be applied to devices such as solar cells, building glass, and greenhouse films, and has a wide range of applications.

[0004] Polymer materials exhibit ideally high emissivity due to the natural molecular bond vibrations in the mid-infrared band. Therefore, improving their reflectivity in the solar band is crucial for achieving radiative cooling. However, due to daytime solar irradiation, the solar irradiation absorbed by the radiative cooling material will negate the effect of radiative cooling. Thus, achieving radiative cooling requires at least 90% of sunlight to be reflected. However, radiative cooling materials are constrained by the following conditions: (1) The rapid development of nanotechnology and metamaterials has enabled researchers to improve radiative cooling performance to a certain extent through structural design using photonic crystals, metamaterials, etc. However, due to the high difficulty and cost of micro-nano fabrication technology, it is difficult to achieve large-scale application; (2) To strongly reflect sunlight, metals such as silver and aluminum are often used as reflective layers. However, prolonged outdoor exposure will cause the metal layer to oxidize and easily generate glare pollution, greatly limiting its application; (3) Metal oxides with high refractive index, such as titanium dioxide, are often used to replace metal reflective layers to reflect sunlight. However, these metal oxides usually have strong absorption of sunlight in the ultraviolet band, which will affect the radiative cooling performance. Therefore, further exploration of technical routes is needed to further improve the performance and application of radiative cooling materials. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of high technical difficulty, high cost, poor radiation cooling performance and difficulty in large-scale application of radiation cooling materials, and to provide a method for preparing radiation cooling thin films based on metal-organic framework UIO-66.

[0006] A method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 is carried out according to the following steps:

[0007] 1. Surface modification of metal-organic framework UIO-66 to obtain surface-modified metal-organic framework UIO-66;

[0008] 2. Mix polydimethylsiloxane and n-hexane evenly to obtain a PDMS solution;

[0009] 3. The surface-modified metal-organic framework UIO-66 is added to the PDMS solution and stirred evenly. Then, the curing agent of PDMS is added and stirred to obtain a stable suspension. The stable suspension is cast on the substrate, cured into a film, and peeled off to obtain a radiation-cooling film based on the metal-organic framework UIO-66.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] I. The preparation process of this invention is simple, low in cost, and has a significant cooling effect;

[0012] II. The radiation-cooling thin film based on metal-organic framework UIO-66 of the present invention uses PDMS as the film-forming material to obtain high emissivity, and UIO-66 as a filler to make up for the lack of reflectivity in the solar band and improve the reflectivity of the radiation-cooling thin film in the solar band.

[0013] III. The radiation-cooling thin film based on the metal-organic framework UIO-66 of the present invention has an average reflectivity of 94.02% in the solar irradiation band (0.3-2.5μm), an average emissivity of 94.60% in the infrared band (2.5-25μm), and an average emissivity of 95.01% in the atmospheric window band (8-14μm).

[0014] The present invention provides a radiation-cooling thin film based on the metal-organic framework UIO-66. Attached Figure Description

[0015] Figure 1 This is a scanning electron microscope image of the metal-organic framework UIO-66 prepared in step one of Example 1;

[0016] Figure 2 The spectral reflectance diagram of the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1;

[0017] Figure 3 The spectral emissivity diagram of the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1;

[0018] Figure 4 A comparison of the external field test temperature and chamber ambient temperature of the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1 and the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Comparative Example 1. Detailed Implementation

[0019] Specific Implementation Method 1: This implementation method describes a method for preparing a radiation-cooling thin film based on a metal-organic framework (UIO-66), which is completed according to the following steps:

[0020] 1. Surface modification of metal-organic framework UIO-66 to obtain surface-modified metal-organic framework UIO-66;

[0021] 2. Mix polydimethylsiloxane and n-hexane evenly to obtain a PDMS solution;

[0022] 3. The surface-modified metal-organic framework UIO-66 is added to the PDMS solution and stirred evenly. Then, the curing agent of PDMS is added and stirred to obtain a stable suspension. The stable suspension is cast on the substrate, cured into a film, and peeled off to obtain a radiation-cooling film based on the metal-organic framework UIO-66.

[0023] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the surface modification method for the metal-organic framework UIO-66 in step one is as follows: The metal-organic framework UIO-66 is dispersed in deionized water, then a hexadecyltrimethylammonium bromide solution is added, the mixture is stirred and reacted, then centrifuged and washed several times, and finally dried to obtain the surface-modified metal-organic framework UIO-66. Other steps are the same as in Specific Implementation Method One.

[0024] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the size of the metal-organic framework UIO-66 is 0.75μm to 1.2μm, and the preparation method is completed according to the following steps:

[0025] ① Prepare a zirconium tetrachloride solution with a concentration of 15 mmol / L using DMF as the solvent;

[0026] ② Prepare a 15 mmol / L terephthalic acid solution using DMF as the solvent;

[0027] ③ Mix 75 mL of a 15 mmol / L zirconium tetrachloride solution and 75 mL of a 15 mmol / L terephthalic acid solution in a blue-capped bottle, then add 0.36 mol of anhydrous acetic acid and sonicate to mix thoroughly to obtain a mixed solution. Filter the mixed solution through a 220 nm syringe filter to remove excess small particulate impurities. React the filtered solution at 120 °C for 12 h. After the reaction is complete, centrifuge at 8000 r / min to collect the product. Wash the collected product three times each with DMF and anhydrous ethanol, and finally dry it at 60 °C to obtain the metal-organic framework UIO-66. Other steps are the same as in specific implementation method one or two.

[0028] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in the following ways: the mass ratio of the metal-organic framework UIO-66, the volume ratio of deionized water to hexadecyltrimethylammonium bromide solution is (1.0g~1.5g):(100mL~150mL):(10mL~15mL); the concentration of the hexadecyltrimethylammonium bromide solution is 5mmol / L; the stirring reaction time is 4h~5h; the centrifugation and washing are performed three times each, using anhydrous ethanol as the solvent; each centrifugation is performed at 8000rpm for 5min. Other steps are the same as in Specific Implementation Methods One to Three.

[0029] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the volume ratio of polydimethylsiloxane to n-hexane in step two is 5:1. The other steps are the same as in Specific Implementation Methods One to Four.

[0030] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the mass ratio of the surface-modified metal-organic framework UIO-66 to the PDMS in the PDMS solution in step three is 1:5. The other steps are the same as in Specific Implementation Methods One to Five.

[0031] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: in step three, the mass ratio of PDMS to the PDMS curing agent is 10:1; and the mixing time of PDMS and the PDMS curing agent is 30 to 60 minutes. Other steps are the same as in Specific Implementation Methods One to Six.

[0032] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the curing time in step three is 60℃~80℃, and the curing time is 10h~12h. The other steps are the same as in Specific Implementation Methods One to Seven.

[0033] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the radiation-cooling thin film based on the metal-organic framework UIO-66 exhibits a high reflectivity of 94.02% in the solar band and a high emissivity of 95.01% in the atmospheric window band. The other steps are the same as in Specific Implementation Methods One to Eight.

[0034] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the radiation-cooling thin film based on the metal-organic framework UIO-66 exhibits radiation-cooling performance with an average midday cooling temperature exceeding 7°C. The other steps are the same as in Specific Implementation Methods One to Nine.

[0035] The beneficial effects of the present invention are verified using the following embodiments;

[0036] Example 1: A method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 is carried out according to the following steps:

[0037] I. Preparation of metal-organic framework UIO-66:

[0038] ① Prepare a zirconium tetrachloride solution with a concentration of 15 mmol / L using DMF as the solvent;

[0039] ② Prepare a 15 mmol / L terephthalic acid solution using DMF as the solvent;

[0040] ③ Mix 75 mL of 15 mmol / L zirconium tetrachloride solution and 75 mL of 15 mmol / L terephthalic acid solution in a blue-capped bottle, then add 0.36 mol of anhydrous acetic acid and sonicate to mix thoroughly to obtain a mixed solution. Filter the mixed solution through a 220 nm syringe filter to remove excess small particulate impurities. Then react the filtered solution at 120 °C for 12 h. After the reaction is complete, centrifuge at 8000 r / min to collect the product. Wash the collected product three times with DMF and anhydrous ethanol, respectively. Finally, dry at 60 °C to obtain the metal-organic framework UIO-66.

[0041] 2. Disperse the metal-organic framework UIO-66 in 100 mL of deionized water, add 10 mL of hexadecyltrimethylammonium bromide solution, stir for 5 h, centrifuge and wash 3 times, and finally dry to obtain the surface-modified metal-organic framework UIO-66.

[0042] The concentration of the hexadecyltrimethylammonium bromide solution mentioned in step two is 5 mmol / L;

[0043] In step two, anhydrous ethanol was used as the solvent for centrifugation and washing; each centrifugation was performed at 8000 rpm for 5 minutes.

[0044] 3. Mix polydimethylsiloxane and n-hexane evenly to obtain a PDMS solution;

[0045] The volume ratio of polydimethylsiloxane to n-hexane mentioned in step three is 5:1;

[0046] 4. The surface-modified metal-organic framework UIO-66 was added to the PDMS solution and stirred evenly. Then, the curing agent of PDMS was added and stirred for 30 minutes to obtain a stable suspension. The stable suspension was cast on an acrylic substrate and cured at 60°C for 12 hours to form a film. The film was then peeled off to obtain a radiation-cooling film based on the metal-organic framework UIO-66.

[0047] The mass ratio of the surface-modified metal-organic framework UIO-66 to PDMS in the PDMS solution in step four is 1:5;

[0048] In step four, the mass ratio of PDMS to PDMS curing agent is 10:1.

[0049] The PDMS and PDMS curing agent described in Example 1 were purchased from Dow Corning Sylgard, Inc., USA, and the product name is 184.

[0050] Comparative Example 1: A method for preparing a zirconium dioxide-based radiation-cooling thin film, which is carried out according to the following steps:

[0051] 1. Mix polydimethylsiloxane and n-hexane evenly to obtain a PDMS solution;

[0052] The volume ratio of polydimethylsiloxane to n-hexane mentioned in step one is 5:1;

[0053] 2. Add zirconium dioxide to PDMS solution, stir evenly, then add PDMS curing agent, stir and mix for 30 min to obtain a stable suspension; cast the stable suspension on an acrylic substrate, cure at 60℃ for 12 h to form a film, peel off to obtain a zirconium dioxide-based radiation cooling film.

[0054] The mass ratio of zirconium dioxide to PDMS in the PDMS solution mentioned in step two is 1:5;

[0055] In step two, the mass ratio of PDMS to PDMS curing agent is 10:1.

[0056] The zirconium dioxide described in Example 1 was purchased from Aladdin Industries, Inc., USA.

[0057] The PDMS and PDMS curing agent described in Example 1 were purchased from Dow Corning Sylgard, Inc., USA, and the product name is 184.

[0058] Figure 1 This is a scanning electron microscope image of the metal-organic framework UIO-66 prepared in step one of Example 1;

[0059] from Figure 1 It can be seen that the particle size of the metal-organic framework UIO-66 prepared in step one is 1.2 μm.

[0060] Figure 2 The spectral reflectance diagram of the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1;

[0061] from Figure 2 It can be seen that the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1 exhibits a high reflectivity of 94.02% in the solar band.

[0062] Figure 3 The spectral emissivity diagram of the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1;

[0063] from Figure 3 It can be seen that the average emissivity of the radiation-cooling thin film based on the metal-organic framework UIO-66 prepared in Example 1 reaches 94.60% in the infrared band.

[0064] Figure 4Comparison of the external field test temperature and chamber ambient temperature of the radiation-cooling thin film based on metal-organic framework UIO-66 prepared in Example 1 and the radiation-cooling thin film based on metal-organic framework UIO-66 prepared in Comparative Example 1.

[0065] from Figure 4 It can be seen that the average cooling temperature of the radiation-cooling film based on the metal-organic framework UIO-66 prepared in Example 1 reaches above 7°C during midday (11:00-14:00), while the average cooling temperature of the radiation-cooling film based on zirconium dioxide prepared in Comparative Example 1 is only about 4°C. Therefore, Example 1 has better radiation-cooling performance.

Claims

1. A method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66, characterized in that... The preparation method is completed according to the following steps:

1. Surface modification of metal-organic framework UIO-66 to obtain surface-modified metal-organic framework UIO-66; 2. Mix polydimethylsiloxane and n-hexane evenly to obtain a PDMS solution; 3. Add the surface-modified metal-organic framework UIO-66 to the PDMS solution, stir evenly, then add the PDMS curing agent, stir and mix to obtain a stable suspension. A stable suspension was cast onto a substrate, solidified into a film, and then peeled off to obtain a radiation-cooling thin film based on the metal-organic framework UIO-66.

2. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... The method for surface modification of metal-organic framework UIO-66 in step one is as follows: disperse metal-organic framework UIO-66 in deionized water, add hexadecyltrimethylammonium bromide solution, stir the reaction, centrifuge and wash several times, and finally dry to obtain surface-modified metal-organic framework UIO-66.

3. A method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1 or 2, characterized in that... The metal-organic framework UIO-66 has a size of 0.75 μm to 1.2 μm, and its preparation method is carried out according to the following steps: ① Prepare a zirconium tetrachloride solution with a concentration of 15 mmol / L using DMF as the solvent; ② Prepare a 15 mmol / L terephthalic acid solution using DMF as the solvent; ③ Mix 75 mL of 15 mmol / L zirconium tetrachloride solution and 75 mL of 15 mmol / L terephthalic acid solution in a blue-capped bottle, then add 0.36 mol of anhydrous acetic acid and sonicate to mix thoroughly to obtain a mixed solution. Filter the mixed solution through a 220 nm syringe filter to remove excess small particulate impurities. Then react the filtered solution at 120 °C for 12 h. After the reaction is complete, centrifuge at 8000 r / min to collect the product. Wash the collected product three times with DMF and anhydrous ethanol, respectively. Finally, dry at 60 °C to obtain the metal-organic framework UIO-66.

4. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 2, characterized in that... The mass ratio of the metal-organic framework UIO-66 to the volume ratio of deionized water and hexadecyltrimethylammonium bromide solution is (1.0g~1.5g):(100mL~150mL):(10mL~15mL); the concentration of the hexadecyltrimethylammonium bromide solution is 5mmol / L; the stirring reaction time is 4h~5h; the centrifugation and washing are performed 3 times each, and anhydrous ethanol is used as the solvent; each centrifugation is performed at 8000 rpm for 5min.

5. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... The volume ratio of polydimethylsiloxane to n-hexane in step two is 5:

1.

6. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... In step three, the mass ratio of the surface-modified metal-organic framework UIO-66 to the PDMS in the PDMS solution is 1:

5.

7. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... In step three, the mass ratio of PDMS to PDMS curing agent is 10:1; the mixing time of PDMS and PDMS curing agent is 30 min to 60 min.

8. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... The curing time in step three is 60℃~80℃, and the curing time is 10h~12h.

9. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... The radiation-cooling thin film based on the metal-organic framework UIO-66 exhibits a high reflectivity of 94.02% in the solar band and a high emissivity of 95.01% in the atmospheric window band.

10. The method for preparing a radiation-cooling thin film based on a metal-organic framework UIO-66 according to claim 1, characterized in that... The aforementioned radiation cooling film based on the metal-organic framework UIO-66 exhibits radiation cooling performance with an average midday cooling temperature of over 7°C.

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