Zeolite adsorption thermal control coating with Li / Cr bimetal active sites and preparation method of zeolite adsorption thermal control coating

Abstract

The invention discloses a zeolite adsorption thermal control coating with Li / Cr bimetal active sites and a preparation method of the zeolite adsorption thermal control coating, and belongs to the field of special functional coatings. The invention aims to solve the problems that a molecular sieve adsorption coating lacks strong adsorption sites and is easy to desorb after adsorbing pollution molecules. The synergistic polarization electric field of alkaline earth metal and transition metal can generate strong complexation with pollutant molecules, so that the adsorption binding capacity of the molecular adsorption coating is improved through the synergistic effect of chemical adsorption and physical adsorption, and the molecular adsorption coating can stably adsorb pollutants. The coating has double functions of adsorption and light absorption, and the pollutant capturing effect is enhanced in cooperation with a polarization electric field. The method can be widely applied to the fields of spacecraft thermal control systems, sewage treatment, pollution protection, air purification and the like, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of special functional coatings. Specifically, it relates to a zeolite adsorption thermal control coating with Li / Cr bimetallic active sites and its preparation method. The coating of the invention has both adsorption and light absorption functions. The invention has broad application prospects in areas such as spacecraft thermal control systems, sewage treatment, pollution prevention, and air purification. Background Art

[0002] As the precision of spacecraft optical and thermal control systems continues to improve, higher requirements are placed on the control of space molecular contaminants. Space molecular contaminants mainly come from pollutant gases released by spacecraft materials. These pollutants form thin films on spacecraft surfaces, affecting the performance of sensitive devices such as optical devices, thermal control coatings, and solar panels. Traditional zeolite molecular sieve materials have been widely used to adsorb volatile organic compounds (VOCs) due to their large specific surface area and pore size. However, the large pore size limits their adsorption capacity for small organic molecule pollutants. In addition, sunlight contains a large amount of thermal energy, and spacecraft directly exposed to sunlight in space absorb a large amount of heat. This can cause the surface temperature of the spacecraft to rise sharply, thereby affecting the performance and lifespan of various instruments and equipment on the spacecraft. Currently, there is a lack of coatings that have the dual functions of absorbing light and adsorbing pollutants.

[0003] While traditional molecular sieve modification methods (such as acid etching and alkaline etching) can regulate the pore structure, they can easily lead to the destruction of the molecular sieve framework structure and a reduction in specific surface area. In addition, traditional coatings lack strong binding force for pollutants, resulting in easy desorption of adsorbed pollutants, affecting the long-term performance of the coating. Therefore, it is of great significance to develop a molecular adsorption coating that can improve the adsorption and binding force of the coating through the synergistic effect of chemical adsorption and physical adsorption. Summary of the Invention

[0004] The present invention aims to address the problem of molecular sieve adsorption coatings lacking strong adsorption sites and being prone to desorption after adsorbing pollutants. The present invention provides a molecular adsorption coating loaded with composite bimetallic ions, Li / Cr-USY zeolite, and a preparation method thereof. The synergistic polarization electric field of the alkaline earth metal and transition metal enables strong complexation with pollutant molecules, enabling them to synergize through chemical and physical adsorption, increasing the adsorption and binding capacity of the molecular adsorption coating, enabling stable adsorption of pollutants.

[0005] The coating of the present invention has dual adsorption and light absorption functions, and the synergistic polarization electric field enhances the capture of pollutants. The present invention has broad application prospects in fields such as spacecraft thermal control systems, sewage treatment, pollution protection and air purification.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The purpose of the present invention is to provide a method for preparing a thermal control coating by adsorbing composite bimetallic ion Li / Cr-USY zeolite molecules, and by providing chemical adsorption sites, the binding force of the coating to adsorb pollutants is improved, so that it can stably adsorb pollutants. The coating of the present invention has both physical adsorption and chemical adsorption when interacting with pollutant molecules, which can significantly improve the adsorption capacity of the coating and achieve a long-term stable adsorption effect. The coating of the present invention includes two parts: a functional filler (zeolite and carbon black) and a binder. The functional coating is synthesized by a template method. Na-USY zeolite is pretreated and then ion-exchanged to load Li / Cr metal particles, and the silica sol is prepared with the binder and carbon black. The composite coating is formed by a spraying process.

[0008] The object of the present invention is to provide a method for preparing a zeolite adsorption thermal control coating with Li / Cr bimetallic active sites, comprising the following steps:

[0009] Step 1: Na-USY zeolite is placed in NH4Cl solution for exchange, washed with deionized water and dried to obtain NH4-USY powder;

[0010] Step 2: fully dissolve lithium chloride and chromium sulfate in deionized water, add NH4-USY zeolite, vigorously stir under microwave-assisted conditions, dry, and calcine to obtain a loaded composite metal ion zeolite;

[0011] Step 3: Mix the composite metal ion zeolite, carbon black and silica sol, and mechanically stir until uniform to obtain a slurry;

[0012] Step 4: remove impurities on the surface of the substrate, evenly coat the slurry on the surface, heat and cure, and obtain the adsorption thermal control coating.

[0013] It is further defined that in step 1, the Na-USY zeolite is prepared according to the following steps:

[0014] Step 1: Add 12g of sodium hydroxide to 360g of deionized water and stir magnetically until completely dissolved. Add 16.4g of sodium aluminate and continue stirring until the sodium aluminate is completely dissolved. Then, slowly add 225g of silica sol while stirring vigorously. After the addition is complete, continue stirring until the mixture is fully mixed.

[0015] Step 2: transfer to a polytetrafluoroethylene-lined hydrothermal reactor, seal it, place it in an oven, and react at 160°C for 48 hours;

[0016] Step 3: After taking out, cool naturally to room temperature, open the reactor, centrifuge at a speed of 8000-10000 r / min for 10-15 minutes, and wash the separated solid product with deionized water several times until the pH of the supernatant is neutral;

[0017] Step 4: vacuum drying at 80°C for 12 hours to obtain Na-USY molecular sieve, or drying at 110°C for 12 hours, heating to 600°C at a rate of 2°C / min, and calcining at this temperature for 6 hours to obtain Na-USY molecular sieve.

[0018] It is further defined that in step 2, the drying is first performed at 60° C. for 2 hours and then at 110° C. for 12 hours.

[0019] It is further defined that in step 2, the temperature is raised to 600° C. at a rate of 2° C. / min in air and the calcination is carried out for 5 hours.

[0020] It is further defined that in step 2, the microwave power is 300W.

[0021] It is further defined that in step 2, the pigment-to-base ratio is 0.2-1; the mass ratio of the composite metal ion zeolite to the carbon black is 1:1; and the mixing and stirring time is 2h-3h.

[0022] It is further defined that in step 2, curing: heating to 60° C. and keeping warm for 1 hour; then heating to 80° C. and keeping warm for 8 hours.

[0023] It is further defined that the preparation process of the coating in step four covers a variety of methods such as spraying, brushing, scraping, and spin coating. The specific method can be selected according to actual needs; the process parameters such as spraying pressure, spraying speed and spray gun distance can be adjusted according to actual needs; the specific spraying parameters are as follows: nozzle diameter is 2.5mm, spray gun pressure is 1.5MPa, spray gun movement speed is 80cm / s, and spray distance is 20cm.

[0024] It is further defined that the base material of the coating can be a metal material such as aluminum alloy, or a non-metallic base such as resin, organic-inorganic composite material, etc.

[0025] It is further defined that in step 4, the method for removing impurities on the surface of the metal substrate is: the surface of the substrate is polished using 500-grit sandpaper, and then placed in anhydrous ethanol for ultrasonic cleaning for 30 minutes to remove surface impurities.

[0026] The coating thickness of the present invention is 150 μm.

[0027] The present invention uses metal ion exchange technology to load composite metal particles into USY zeolite to prepare a molecular adsorption thermal control coating with high adsorption binding force and light absorption ability. The present invention has the following beneficial effects:

[0028] (1) The USY zeolite prepared by the template method has a microporous and mesoporous multi-level structure and metal ion chemical adsorption sites, which can provide more adsorption sites under low-pressure environment and improve the low-pressure adsorption performance of the coating.

[0029] (2) By loading composite metal ions into the zeolite pores through ion exchange, the presence of Li+ can affect the diffusion rate of pollutants within the zeolite particles. Because Li+ changes the electric field and chemical environment within the zeolite pores, the migration resistance of pollutant ions within the pores changes; after Cr ions are exchanged into the zeolite lattice, they can interact with organic pollutants with π electron systems through π-π interactions and bind to pollutant molecules through electrostatic interactions.

[0030] (3) Through the synergistic effect of chemical adsorption and physical adsorption, the coating can stably adsorb spatial molecular pollutants for a long time, reduce the desorption of pollutants, and improve adsorption stability.

[0031] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a SEM image of the modified zeolite molecular sieve prepared by the method of Example 1;

[0033] Figure 2 is the XRD pattern of the modified zeolite molecular sieve prepared by the method of Example 1;

[0034] Figure 3 FIG1 is a nitrogen isothermal adsorption-desorption diagram of the modified zeolite molecular sieve prepared by the method of Example 1;

[0035] Figure 4 is a SEM image of the modified zeolite molecular sieve coating prepared by the method of Example 1;

[0036] Figure 5 This is the Fourier transform infrared absorption spectrum test result of the modified zeolite molecular adsorption coating prepared by the method of Example 1;

[0037] Figure 6 This is the UV-visible spectrometer test result of the modified zeolite molecular adsorption coating prepared by the method of Example 1;

[0038] Figure 7 These are the actual pictures of the modified zeolite molecular adsorption coating prepared by the method of Example 1 before and after the hot and cold alternating experiment. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art further understand the present invention and are not intended to limit the present invention in any way. It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention. These modifications and improvements are all within the scope of protection of the present invention.

[0040] Example 1: The preparation method of the zeolite adsorption thermal control coating with Li / Cr bimetallic active sites in this embodiment is achieved by the following steps:

[0041] (1) Preparation of Na-USY zeolite:

[0042] Na-USY zeolite was synthesized by a hydrothermal method. The specific steps are as follows: 360 g of deionized water was added to a beaker, 12 g of sodium hydroxide was added to the water, and stirred with a magnetic stirrer until completely dissolved.

[0043] Add 16.4 g of sodium aluminate to the above sodium hydroxide solution and continue stirring until the sodium aluminate is completely dissolved. At this time, the solution may be slightly clear or slightly turbid.

[0044] Slowly add 225 g of silica sol to the above solution while stirring vigorously to prevent excessive local concentration from causing uneven gelation.

[0045] After the dropwise addition was completed, stirring was continued for 2 hours to ensure that the solution was fully mixed and uniform to obtain a gel.

[0046] The prepared gel was transferred to a polytetrafluoroethylene-lined hydrothermal reactor with a filling degree not exceeding 80% to prevent excessive pressure during the reaction.

[0047] The reactor was sealed and placed in an oven, the oven temperature was set to 160°C, and the reaction time was 48 hours. After the reaction was completed, the reactor was removed from the oven and naturally cooled to room temperature. The reactor was opened, the product was transferred to a centrifuge tube, and the tube was centrifuged at a speed of 10,000 r / min for 10 minutes to separate the solid product. The solid product was washed with deionized water multiple times, and centrifuged after each washing until the pH of the supernatant was close to neutral. The washed solid product was transferred to a watch glass, placed in a vacuum drying oven, and dried at 80°C for 12 hours to obtain Na-USY molecular sieve.

[0048] (2) Na-USY zeolite pretreatment

[0049] The NH4Cl solution was used to exchange with Na-USY at 80 °C for 4 hours. After the exchange, it was washed with deionized water and then dried at 110 °C to obtain NH4-USY powder.

[0050] (3) Loading composite metal particles

[0051] 0.1M lithium chloride and 0.1M chromium sulfate were fully dissolved in 100ml of deionized water, followed by the addition of 10g of NH4-USY zeolite. The thick paste was mixed and vigorously stirred for 30 minutes under microwave-assisted microwave conditions at a power of 300W. Subsequently, the zeolite underwent a drying process at 60°C in an oven for 2 hours, followed by a second drying stage at 110°C for 12 hours. The Li / Cr-USY sample was obtained after calcination at 600°C in air at a heating rate of 2°C / min for a duration of 5 hours to obtain the loaded composite metal ion zeolite.

[0052] (4) Configuration of molecular adsorption coating spray slurry

[0053] Accurately weigh 7.5g of zeolite, 7.5g of carbon black, and 50g of silica sol into a mixing container. Stir at a constant speed with a mechanical stirrer at room temperature for 30 minutes to ensure that the zeolite, carbon black, and silica sol are thoroughly mixed and form a uniform suspension to obtain a spray slurry.

[0054] (5) Spraying of molecular adsorption coating

[0055] In this example, aluminum alloy sheet was used as the substrate material. First, the substrate surface was polished with 500-grit sandpaper and then ultrasonically cleaned in anhydrous ethanol for 30 minutes to remove surface impurities. The prepared spray slurry was evenly sprayed onto the aluminum alloy substrate using the following spraying parameters: nozzle diameter 2.5 mm, spray gun pressure 1.5 MPa, spray gun travel speed 80 cm / s, and spray distance 20 cm. To ensure coating uniformity and density, multiple spraying processes were employed, with each spraying allowing the coating surface to air-dry before the next spraying. After spraying, the coating sample was placed in a vacuum oven for programmed temperature curing to enhance the adhesion between the coating and the substrate. The curing program for a spray thickness of 150 μm was as follows: first, heating to 60°C at a set rate and holding for 1 hour; then, heating to 80°C and holding for 8 hours. After the above process, an adsorption coating with excellent adsorption properties and good stability was obtained.

[0056] The SEM test results of the USY zeolite loaded with composite metal ions obtained in this example are as follows: Figure 1 shown.

[0057] The XRD test results of the composite metal ion loaded USY zeolite obtained in this example are as follows: Figure 2 As shown, the diffraction peak positions of the ion-exchanged zeolite and the CHA zeolite characterization cards and the original are basically consistent, indicating that it has the crystal structure of FAU zeolite, and the zeolite after ion exchange has good crystallinity.

[0058] The test results of the nitrogen adsorption-desorption curve of USY zeolite loaded with composite metal ions at 77.3K obtained in this example are shown in the figure. Figure 3 As shown in the figure, the zeolite has an obvious hysteresis loop, indicating that it has a mesoporous structure, but the micropores are dominant. According to the BET method, its specific surface area is calculated from 691.26 cm before etching to 2 / g dropped to 674.17cm 2 / g, which increases the mesopore volume, making it more conducive to the adsorption of pollutant molecules.

[0059] The scanning electron microscope test results of the USY zeolite adsorption thermal control coating loaded with composite metal ions obtained in this embodiment are as follows: Figure 4 As shown, the coating surface has a hierarchical porous rough structure, which is conducive to the adsorption of spatial molecular pollutants.

[0060] The Fourier transform infrared absorption spectrum test of the composite metal ion molecular sieve adsorption thermal control coating and the original zeolite coating obtained in this embodiment is as follows: Figure 5 As shown, it is calculated that the average emissivity of the coating in the wavelength range of 2 to 16 μm is 97.7% and 97.6% respectively.

[0061] The UV-visible spectrometer test results of the composite metal ion molecular sieve adsorption thermal control coating and the original zeolite coating obtained in this embodiment are as follows: Figure 6 As shown, it is calculated that within the wavelength range of 200 to 2500 nm, the average solar absorptivity is 98.1% and 98.04% respectively.

[0062] The adsorption coating obtained in this embodiment was subjected to a hot and cold cycle test. The coating was placed in a vacuum high and low temperature tester and subjected to a hot and cold alternation test at -200 to 200°C. Figure 7 By comparison, the coating after the test showed no cracking or powdering on the substrate and still had excellent interfacial bonding strength.

[0063] The molecular adsorption coating material obtained in Example 1 and the typical molecular contaminant dioctyl phthalate were placed in a vacuum test system for space molecular contamination, with the heating stage set at 65°C. The adsorption experiment was conducted on the heating stage, with samples taken every hour and weighed ex situ on a precision balance. The adsorption capacity was calculated by calculating the difference between the before and after weighing. The results are shown in the following table:

[0064] Table 1 Adsorption test results of loaded composite metal ion molecular sieve adsorption thermal control coating

[0065] Adsorption time <![CDATA[Adsorption capacity (mg / cm 2 )]]> 1h 1.4766 2h 2.5179 3h 3.3670 4h 4.0267 5h 5.3964 6h 6.2876

[0066] As shown in Table 1, the adsorption coating has a strong adsorption capacity for space molecular pollutants. The adsorption reaches saturation in 6 hours, and the adsorption capacity is 6.2876 mg / cm 2 The adsorption capacity before modification was 3.8143 mg / cm 2 , the adsorption capacity is greatly improved compared with that before modification.

[0067] The above describes the specific embodiments of the present invention. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a zeolite adsorption thermal control coating with Li / Cr bimetallic active sites, characterized in that: The following steps are involved: Step 1: Na-USY zeolite is placed in NH4Cl solution for exchange, washed with deionized water and dried to obtain NH4-USY powder; Step 2: fully dissolve lithium chloride and chromium sulfate in deionized water, add NH4-USY zeolite, vigorously stir under microwave-assisted conditions, dry, and calcine to obtain a loaded composite metal ion zeolite; Step 3: Mix the composite metal ion zeolite, carbon black and silica sol, and mechanically stir until uniform to obtain a slurry; Step 4: remove impurities on the surface of the substrate, evenly coat the slurry on the surface, heat and cure, and obtain the adsorption thermal control coating.

2. The method according to claim 1, characterized in that Na-USY zeolite is prepared according to the following steps: Step 1: Add 12g of sodium hydroxide to 360g of deionized water and stir magnetically until completely dissolved. Add 16.4g of sodium aluminate and continue stirring until the sodium aluminate is completely dissolved. Then, slowly add 225g of silica sol while stirring vigorously. After the addition is complete, continue stirring until the mixture is fully mixed. Step 2: transfer to a polytetrafluoroethylene-lined hydrothermal reactor, seal it, place it in an oven, and react at 160°C for 48 hours; Step 3: After taking out, naturally cool to room temperature, open the reactor, centrifuge at a speed of 8000-10000 rpm for 10-15 minutes, and wash the separated solid product with deionized water several times until the pH of the supernatant is neutral; Step 4: vacuum drying at 80°C for 12 hours to obtain Na-USY molecular sieve, or drying at 110°C for 12 hours, heating to 600°C at a rate of 2°C / min, and calcining at this temperature for 6 hours to obtain Na-USY molecular sieve.

3. The method according to claim 1, characterized in that In step 2, drying is first performed at 60° C. for 2 h and then at 110° C. for 12 h.

4. The method according to claim 1, characterized in that In step 2, the temperature is raised to 600° C. at a rate of 2° C. / min in air and calcined for 5 h.

5. The method according to claim 1, characterized in that: In step 2, the microwave power is 300W.

6. The method according to claim 1, characterized in that In step 3, the pigment-to-base ratio is 0.2-1; the mass ratio of the composite metal ion zeolite to the carbon black is 1:

1.

7. The method according to claim 1, characterized in that: In step 4, curing: heating to 60°C and keeping warm for 1 hour; then heating to 80°C and keeping warm for 8 hours.

8. The method according to claim 1, characterized in that: The coating is carried out by spraying, brushing, knife coating or spin coating.

9. The method according to claim 1, characterized in that: The base materials are aluminum alloy, resin, and organic-inorganic composite materials.

10. An adsorptive thermal control coating prepared by the method according to any one of claims 1 to 9.

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