A controllable preparation method for ultrasonic-assisted in-situ etching of molecular sieves and adsorption of thermal control coatings

Abstract

The present invention discloses a controllable preparation method for ultrasonically assisted in-situ etching of molecular sieves and adsorption thermal control coatings, which belongs to the field of special functional coatings. The present invention aims to solve the problems that the pore structure size of the molecular sieve adsorption coating does not match the pollutant molecules, the specific surface area and micropore volume are low, and the adsorption and capture effect is poor. The functional filler of the present invention is to conduct multiple ion exchanges between nano 13X zeolite molecular sieves and ammonium chloride aqueous solution; then, in-situ etching with low-concentration ammonium fluoride aqueous solution is carried out under ultrasonic-assisted conditions, solid-liquid separation, cleaning, drying, and grinding to complete the process. The coating includes two parts: a functional filler and a binder. The functional filler is composed of ultrasonically assisted in-situ etching zeolite powder and zinc oxide, and the binder is silica sol. The composite coating is formed by a spraying process. The present invention has very broad application prospects in the fields of air purification, sewage treatment, aerospace and military industry, pollution protection, etc.

Description

Technical Field

[0001] This invention belongs to the field of special functional coatings, specifically a method for ultrasonically assisted in-situ etching of molecular sieves and a controllable preparation method for adsorption thermal control coatings. It has broad application prospects in air purification, sewage treatment, aerospace, pollution prevention, and other fields. Background Art

[0002] Once in orbit, spacecraft are exposed to a high vacuum environment. The materials used in spacecraft release volatile organic gas molecules, which can severely contaminate sensitive surfaces such as optics, electronics, detectors, and thermal control. On-orbit molecular contamination can degrade the performance of spacecraft hardware and shorten its service life. With increasingly stringent requirements for spacecraft quality and reliability, contamination control has become a critical factor in the success of most space missions. Currently, an effective solution for contamination control is adsorption. Molecular adsorption coatings can be sprayed directly onto the interior surfaces of spacecraft, offering advantages such as high effectiveness and low power consumption.

[0003] Zeolite molecular sieves are the key adsorption material in molecular adsorption coatings. Their specific surface area, micropore volume, and pore structure are crucial, directly affecting the coating's adsorption capacity for pollutant molecules in a vacuum environment. Etching can be used to manipulate the zeolite molecular sieve framework structure, but traditional etching methods such as acid and alkaline etching can easily damage and collapse the zeolite framework and reduce its specific surface area. Therefore, it is of great significance to develop an ultrasound-assisted in-situ etching molecular sieve adsorption thermal control coating to fine-tune the zeolite micropore structure, increase its specific surface area and micropore volume, and enhance its adsorption capacity. Summary of the Invention

[0004] The present invention aims to address the problem of molecular sieve adsorption coatings with pore size mismatched with pollutant molecules, resulting in low specific surface area and micropore volume, and poor adsorption and capture performance. This invention provides a controllable preparation method for molecular sieve adsorption thermal control coatings by ultrasonically assisted in-situ etching. This method precisely regulates the zeolite molecular sieve pore structure, increases its specific surface area and micropore volume, and enhances its adsorption and capture capacity.

[0005] The purpose of the present invention is to provide a method for preparing an ultrasonically assisted in-situ etching molecular sieve adsorption thermal control multifunctional coating, and a method for matching the zeolite pore structure with pollutant molecules by etching to increase the specific surface area and adsorption capacity.

[0006] The present invention provides a multifunctional coating for ultrasonically assisted in-situ etched molecular sieves and adsorption thermal control, which possesses both adsorption and thermal control properties. The coating comprises a functional filler and a binder. The functional filler is composed of ultrasonically assisted in-situ etched zeolite powder and zinc oxide, and the binder is silica sol. The composite coating is formed by a spraying process.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for ultrasonically assisted in-situ etching of molecular sieves, which is achieved by the following steps:

[0009] Step 1, performing multiple ion exchanges between nano 13X zeolite molecular sieve and ammonium chloride aqueous solution;

[0010] Step 2: Then, in-situ etching with a low-concentration ammonium fluoride aqueous solution is performed under ultrasonic-assisted conditions, followed by solid-liquid separation, cleaning, drying, and grinding. The process is complete.

[0011] The present invention also provides a controllable preparation method for an adsorption thermal control coating, specifically, the 13X zeolite molecular sieve powder treated by the above method is mixed with zinc oxide as a functional filler and silica sol to form a spray slurry; then it is coated on the surface of a substrate and heated and cured to obtain an adsorption thermal control multifunctional coating; wherein the ratio of zeolite powder, zinc oxide powder and silica sol is 1: (0.5~2.5): (2~5).

[0012] It is further defined that the nano 13X zeolite molecular sieve in step 1 is synthesized by gel hydrothermal method. The specific steps are as follows:

[0013] Solution A (silicon source): Sodium silicate was first prepared by dissolving sodium hydroxide, silica sol and water at 90° C. with stirring for 15 minutes.

[0014] Solution B (aluminum source): Sodium silicate was prepared by dissolving sodium aluminate, sodium hydroxide, and water at room temperature with stirring for 30 minutes.

[0015] Solution A was slowly added to solution B under vigorous stirring until a homogeneous gel was obtained.

[0016] The mixture was aged at room temperature for 1-5 days, with 3 days being the optimal time.

[0017] The mixture was then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and crystallized at 80°C-150°C for 8-48 hours. The solid product was separated by centrifugation, washed 3-5 times with distilled water until the pH reached 7-8, and dried at 80°C for 12 hours to obtain a nano-13X zeolite molecular sieve.

[0018] It is further defined that the concentration range of the ammonium chloride solution in step 1 is 0.5 to 2.0 mol / L.

[0019] It is further defined that the mass ratio of the zeolite to the ammonium chloride solution in step 1 is (1:5)-(1:20).

[0020] It is further defined that the ion exchange time in step 1 is 1 h to 5 h, the temperature is 25° C. to 80° C., and the number of reactions can be adjusted according to actual needs.

[0021] It is further defined that the mass concentration range of the ammonium fluoride solution in step 2 is 0.1% to 15%.

[0022] It is further defined that the mass ratio of the zeolite to the ammonium fluoride solution in step 2 is (1:3)-(1:15).

[0023] It is further defined that the temperature for the ultrasonic-assisted low-concentration ammonium fluoride in-situ etching in step 2 includes but is not limited to an ice-water bath at 4°C, room temperature at 25°C, and high temperatures at 50°C and 80°C.

[0024] It is further defined that the time range of the ultrasonic-assisted low-concentration ammonium fluoride in-situ etching in step 2 is 1 to 60 minutes.

[0025] It is further defined that the ratio of zeolite powder, zinc oxide powder and silica sol is 1:0.5-2.5:2-5, and the stirring and mixing time is 3h-15h.

[0026] It is further defined that the coating substrate used can be a metal substrate such as aluminum alloy; it can also be a resin substrate or an organic-inorganic composite material substrate.

[0027] It is further defined that the coating preparation process used includes but is not limited to spraying, brushing, blade coating, spin coating and the like.

[0028] It is further defined that the coating is composed of multiple layers and the thickness can be 20-300 microns.

[0029] It is further defined that zeolite coatings with different morphologies and structures can be prepared by controlling different formulation processes, including process parameters such as spraying pressure, spraying speed and spray gun distance.

[0030] The present invention provides an ultrasonically assisted in-situ etched molecular sieve adsorption thermal control multifunctional coating, which has both adsorption performance and thermal control performance. The present invention has the following beneficial effects:

[0031] (1) Ultrasonic-assisted in-situ ammonium fluoride etching is used to regulate the pore structure of zeolite molecular sieves, open the octahedral cage structure of zeolite molecular sieves, and make the pore structure match the size of molecular pollutants, which is conducive to the binding of pollutant molecules to zeolite.

[0032] (2) The micropore volume, specific surface area and mesopore volume of the zeolite molecular sieve are increased by ultrasound-assisted in-situ ammonium fluoride etching method, thereby promoting the adsorption and diffusion of pollutant molecules in the zeolite molecular sieve.

[0033] (3) Etched zeolite molecular sieve materials, zinc oxide and silica particles are organically combined to form polyhedral crystals and synergistically matched with porous composite structures to effectively scatter sunlight and achieve thermal control requiring low solar absorptivity and high solar emissivity.

[0034] 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

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

[0036] Figure 2 is a TEM image of the etched zeolite molecular sieve prepared by the method of Example 1;

[0037] Figure 3 is the XRD pattern of the etched zeolite molecular sieve prepared by the method of Example 1;

[0038] Figure 4 is the nitrogen isothermal adsorption-desorption curve of the etched zeolite molecular sieve prepared by the method of Example 1;

[0039] Figure 5 is a SEM image of the etched zeolite molecular adsorption coating prepared by the method of Example 1;

[0040] Figure 6 This is the UV-visible spectrometer test result of the etched zeolite molecular adsorption coating prepared by the method of Example 1;

[0041] Figure 7 This is the Fourier transform infrared absorption spectrum test result of the etched zeolite molecular adsorption coating prepared by the method of Example 1;

[0042] Figure 8 These are the actual pictures of the etched zeolite molecular adsorption coating prepared by the method of Example 1 before and after the hot and cold alternating experiment. DETAILED DESCRIPTION

[0043] 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.

[0044] Example 1

[0045] (1) Preparation of Nano-13X Zeolite Molecular Sieve

[0046] Nano-sized zeolite 13X was synthesized using a gel hydrothermal method. The specific steps are as follows: Solution A (silicon source): Sodium silicate was first prepared by dissolving 4.8 g of sodium hydroxide, 15 g of silica sol, and 40 g of water at 90°C with stirring for 15 minutes. Solution B (aluminum source): Sodium silicate was prepared by dissolving 5.5 g of sodium aluminate, 2.1 g of sodium hydroxide, and 40 g of water at room temperature with stirring for 30 minutes. Solution A was slowly added to Solution B under vigorous stirring until a uniform gel was obtained. The final composition of the gel was 3.6 Na₂O:1 Al₂O₃:3 SiO₂:150 H₂O. The mixture was aged at room temperature for one day. The mixture was then transferred to a Teflon-lined stainless steel autoclave and crystallized at 80°C for 12 hours. The solid product was isolated by centrifugation, washed 3-5 times with distilled water until the pH reached 7-8, and dried at 80°C for 12 hours.

[0047] (2) Nano 13X zeolite ion exchange

[0048] Zeolite 13X was ion-exchanged three times with a 1 mol / L aqueous ammonium chloride solution, using a liquid:solid ratio of 20 (mass ratio). The ion exchanges were performed under vigorous stirring at 353K for 3 hours each. The sample was thoroughly rinsed with deionized water after each ion exchange. The solid product was washed 3-5 times with deionized water and dried at 373K for 6 hours. The resulting ammonia-exchanged zeolite was used for subsequent processing.

[0049] (3) Ultrasonic-assisted in-situ etching of nano-13X zeolite molecular sieves using low-concentration ammonium fluoride

[0050] Accurately weigh 2.0g of ammonium fluoride and add it to 48.0g of water (mass concentration 4%). Stir the ammonium fluoride aqueous solution in an ice-water bath to fully dissolve it for later use. Accurately weigh 5.0g of 13X ammonia-exchanged zeolite and add it to the ammonium fluoride aqueous solution (the mass ratio of liquid to solid is 10). Stir at high speed in an ice-water bath to carry out the etching reaction. After reacting for 10 minutes, immediately perform solid-liquid separation by suction filtration. Rinse thoroughly 3-5 times with hot distilled water preheated at 353K to remove fluoride ions in the solution to obtain a solid etching product. Dry the etching product at 373K for 6 hours and grind it to obtain zeolite powder.

[0051] (4) Configuration of molecular adsorption coating spray slurry

[0052] The zeolite powder, zinc oxide powder and silica sol obtained in step (3) were accurately weighed in a mass ratio of 1:1:2, a small amount of deionized water was added to the silica sol, and magnetic stirring was performed at room temperature for 30 minutes to mix evenly; in order to prevent the zeolite from being poorly dispersed or agglomerated due to too fast an addition speed, the 13X zeolite and zinc oxide powder were fully ground and mixed evenly, and then slowly added to the diluted silica sol in batches several times, and stirring was continued for 10 hours.

[0053] Wherein, in step (4), deionized water is added at a mass ratio of silica sol to deionized water of 3:1.

[0054] (5) Spraying and curing of adsorption coating

[0055] In this embodiment, an aluminum alloy sheet is used as the substrate, and the surface of the substrate is polished with 500-mesh sandpaper, and then ultrasonically cleaned with anhydrous ethanol for 30 minutes. The slurry used for spraying is added to the liquid storage tank of the ultrasonic-assisted thermal spraying device, the ultrasonic power is adjusted to 1000W, and ultrasonic action is performed for 25 minutes. The cavitation effect of the ultrasonic wave is used to promote further uniform mixing of the slurry. The spray diluent is sprayed on the surface of the aluminum alloy substrate. The spraying conditions are: the nozzle diameter is 2.5mm, the liquid delivery pressure is 0.6Mpa, the moving speed of the spray gun is 120cm / s, and the spray distance is 20cm. In order to prevent cracking caused by poor coating adhesion, the coating is prepared by multiple spraying methods, with an interval of 5 minutes between each spraying. The obtained graded FAU zeolite adsorption coating is placed in a vacuum oven for programmed temperature heating and curing to ensure strong bonding between the adsorption coating and the substrate and prevent the coating from cracking. The specific heating conditions are: first increase the temperature to 100°C at a rate of 2°C / min, maintain for 1 hour, then increase the temperature to 130°C at a rate of 1°C / min, maintain for 8 hours, and a molecular adsorption coating with good performance can be obtained.

[0056] The scanning electron microscope test results of ultrasonic-assisted ammonium fluoride in-situ etching of zeolite obtained in this example are as follows: Figure 1 As shown, the surface of the zeolite after etching presents a rough structure and an approximately spherical structure, indicating that etching causes significant changes in the surface morphology of the zeolite.

[0057] The transmission electron microscope test results of ultrasonic-assisted ammonium fluoride in-situ etching of zeolite obtained in this example are as follows: Figure 2 As shown in Figure 2, the etched molecular sieve exhibits the typical octahedral structure of FAU zeolite. The effect of etching on the pore structure was observed, and a mesoporous structure appeared inside the etched zeolite.

[0058] The XRD test results of the ultrasonic-assisted ammonium fluoride in-situ etching of zeolite obtained in this example are as follows: Figure 3 As shown, the diffraction peak positions of the etched zeolite and the FAU zeolite characterization cards and the original are basically consistent, indicating that it has the crystal structure of FAU zeolite and the etched zeolite has good crystallinity.

[0059] The nitrogen adsorption-desorption curve test results of the ultrasonic-assisted ammonium fluoride in-situ etching of zeolite at 77.3K obtained in this example are shown in FIG. Figure 4As shown in the figure, the etched zeolite has an obvious hysteresis loop in the range of p / p0 of 0.6-0.8, indicating that it has a mesoporous structure. The hierarchical pore structure of micropores and mesopores is conducive to the transport and diffusion of molecules. According to the BET method, its specific surface area is calculated from 683m 2 / g increased to 891.4m 2 / g, the large specific surface area is conducive to the adsorption of pollutant molecules.

[0060] The scanning electron microscope test results of the ultrasonic assisted in-situ etching of the molecular sieve adsorption thermal control coating obtained in this embodiment are as follows: Figure 5 As shown, the coating surface has a hierarchical porous rough structure, which is conducive to the adsorption of spatial molecular pollutants.

[0061] The UV-visible spectrometer test results of the ultrasonic-assisted in-situ etching of the molecular sieve adsorption thermal control coating obtained in this embodiment are as follows: Figure 6 As shown, it is calculated that the average solar absorptivity is 12.3% in the wavelength range of 200 to 2500 nm.

[0062] The Fourier transform infrared absorption spectrum test of the ultrasonic assisted in-situ etching molecular sieve adsorption thermal control coating obtained in this embodiment is as follows: Figure 7 As shown, it is calculated that the average emissivity of the coating in the wavelength range of 2 to 16 μm is 95.1%.

[0063] 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 8 By comparison, the coating after the test showed no cracking or powdering on the substrate and still had excellent interfacial bonding strength.

[0064] The molecular adsorption coating material obtained in Example 1 and the typical molecular contaminant octadecyl alcohol were placed in a vacuum test system for space molecular contamination, with the heating stage set at 80°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:

[0065] Table 1 Adsorption test results of ultrasonic-assisted in-situ etching molecular sieve adsorption thermal control coating

[0066] Adsorption time <![CDATA[Adsorption capacity (mg / cm 2 )]]> 1h 1.6766 2h 2.5149 3h 3.3678 4h 4.0167 5h 4.3974 6h 4.4876

[0067] 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 4.4876 mg / cm 2 .

[0068] 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 ultrasonically assisted in-situ etching of molecular sieves, characterized in that: The method is achieved by the following steps: Step 1, performing multiple ion exchanges between nano 13X zeolite molecular sieve and ammonium chloride aqueous solution; The concentration of the ammonium chloride aqueous solution is 0.5 mol / L~2.0 mol / L, and the mass ratio of zeolite to the ammonium chloride aqueous solution is 1:(5-20); Step 2: Then, in situ etching with a low concentration of ammonium fluoride aqueous solution is performed under ultrasonic-assisted conditions, followed by solid-liquid separation, cleaning, drying, and grinding. The mass concentration of the ammonium fluoride aqueous solution is 0.1% to 15%, and the mass ratio of zeolite to the ammonium fluoride aqueous solution is 1:(3-15); The etching reaction is carried out at 4°C-80°C with high-speed stirring for 1 min to 60 min.

2. The method according to claim 1, characterized in that In step 1, the mass ratio of liquid to solid is 20.

3. The method according to claim 1, characterized in that The ion exchange is carried out under conditions of vigorous stirring and a temperature of 25°C-80°C, and each time lasts for 1h-5h.

4. The method according to claim 1, characterized in that After each ion exchange, the samples were washed with deionized water 3–5 times and dried at 373 K for 6 h.

5. A controllable preparation method of an adsorption thermal control coating, characterized in that: The method comprises: mixing 13X zeolite molecular sieve powder treated by the method according to any one of claims 1 to 4 with zinc oxide as a functional filler and silica sol to form a spray slurry; then coating the slurry on the surface of a substrate, and heating and curing the slurry to obtain an adsorption thermal control multifunctional coating; wherein the mass ratio of the zeolite powder, the zinc oxide powder and the silica sol is 1: (0.5-2.5): (2-5).

6. The method according to claim 5, characterized in that The coating is carried out by spraying, brushing, knife coating or spin coating.

7. The method according to claim 5, characterized in that The coating was prepared by multiple ultrasonic thermal spraying with an ultrasonic power of 1000 W, a time of 25 min, and an interval of 5 min between each spraying. The spraying conditions were as follows: nozzle diameter of 2.5 mm, liquid feeding pressure of 0.6 MPa, movement speed of the spray gun of 120 cm / s, and spray distance of 20 cm.

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