A warm cloud catalyst and a method for preparing the same

Abstract

The present application relates to a kind of warm cloud catalyst and its preparation method, belong to artificial weather modification catalyst technical field, to solve at least one of the problems such as poor hygroscopicity, poor catalytic performance, low dispersion performance, high relative humidity of starting to absorb moisture of warm cloud catalyst prepared by existing method.The warm cloud catalyst prepared by the method of the present application is a single-layer coated SiO2 structure formed with NaCl core, and the surface of the prepared SiO2 nanomaterial contains hydroxyl (-OH), which can form hydrogen bonds with water, thereby more easily adsorbing water vapor, forming local high humidity on the surface of NaCl, promoting the growth of NaCl hygroscopicity.The particle size of NaCl meets the requirements of 1-10 μm for warm cloud artificial weather modification catalyst materials, which is the basis for good warm cloud artificial weather modification catalyst.

Description

Technical Field

[0001] This invention relates to the field of weather modification catalysts, and more particularly to a warm cloud catalyst and its preparation method. Background Technology

[0002] Against the backdrop of global climate change, increased greenhouse gas emissions have led to global warming, more frequent climate anomalies, increased uneven distribution of precipitation, and a rise in extreme weather events, significantly impacting people's lives and livelihoods and social harmony. Furthermore, there are also problems related to water resources, including a growing global water shortage, uneven distribution of freshwater resources, prominent regional water scarcity, and intensified water supply-demand imbalances. These pose serious challenges to agricultural production and urban water supply, such as water shortages during the wheat growing season, irrigation water shortages for cotton, severe water scarcity, and seasonal water shortages.

[0003] Atmospheric water vapor, as a natural resource, accounts for approximately 10% of the freshwater in all rivers and lakes on Earth. Utilizing weather modification catalysts as cloud condensation nuclei (CCNs) is an effective method to accelerate water droplet formation, which is then collected through rainfall. Therefore, artificial rainmaking is of significant practical importance for ensuring agricultural production, maintaining favorable weather conditions for large-scale international events, and preventing extreme weather events. Currently, weather modification catalysts are mainly classified into three categories: refrigerants, artificial ice nuclei, and hygroscopic nuclei. Refrigerants sublimate or vaporize within clouds, absorbing heat in the process and significantly lowering the surrounding air temperature, causing the air humidity to reach a supersaturated state. This promotes water vapor sublimation to form ice crystals and simultaneously disrupts the metastable state of supercooled water droplets in the cloud, triggering their spontaneous nucleation and freezing. This activates naturally existing ice nuclei within the cloud into ice. Commonly used refrigerants include dry ice (solid CO2), liquid carbon dioxide (LC), liquid nitrogen (LN), and liquid propane (LP). Artificial ice nuclei are weather modification catalysts targeting cold clouds, i.e., clouds with temperatures below 0°C. Currently, the most commonly used artificial ice nuclei are silver iodide (AgI) and modified doped materials based on AgI. The main reason AgI can exert its ice nucleation activity is believed to be its hexagonal crystal lattice structure, which is very similar to ice crystals, making it easier for ice crystals to form on its surface, thus catalyzing the cold cloud precipitation process. Hygroscopic nuclei are generally used for warm clouds, i.e., clouds with temperatures above 0°C. Hygroscopic nuclei can adsorb water vapor in warm clouds, eventually converting it completely into water droplets. These droplets grow through collisions and aggregation until they become large enough to fall like rain. Commonly used materials for warm cloud catalysis include sodium chloride (NaCl), calcium chloride (CaCl2), urea (NH2CONH2), and ammonium nitrate (NH4NO3).

[0004] Sodium chloride (NaCl), a typical water-soluble, hygroscopic warm cloud seeding material, has been used in weather modification for decades. Its superior performance and low cost make it an important material for both research and practical applications. Compared to cold cloud seeding materials, NaCl exhibits broader applicability in warm clouds. For example, although dry ice can function as a refrigerant in artificial rainmaking, its high cost and potential environmental hazards as a greenhouse gas make it unsuitable for green and sustainable development. Furthermore, artificial ice core materials (such as silver iodide, AgI) remain highly controversial in terms of environmental risk assessment. AgI may release silver nanoparticles and elemental iodine during decomposition, substances with strong toxicological effects on human health and ecosystems, and large-scale use would lead to excessively high costs.

[0005] Therefore, selecting a seeding material that is both highly efficient and environmentally friendly has become a research hotspot. Besides NaCl, other warm cloud weather modification catalysts, such as zeolites, silica gel, and metal-organic frameworks (MOFs), have also been proposed for exploration. Although these materials possess certain hygroscopic and catalytic properties, their water adsorption capacity is relatively low, and they also face problems such as high production costs and complex preparation processes. Furthermore, these materials exhibit significant water release characteristics, further limiting their applications. Therefore, the application of NaCl in artificial rainfall processes is constrained by its hygroscopic properties, especially in environments with relative humidity (RH) below ~75%, where the hygroscopic properties of NaCl crystals are not significant, particularly below 25% RH, where almost no detectable water vapor adsorption occurs. This limitation severely affects the widespread application of NaCl as a warm cloud seeding material. To address this issue, researchers have also tried various methods to improve the hygroscopic properties of NaCl. For example, the hygroscopicity of NaCl can be improved by mechanically mixing it with other highly hygroscopic salts (such as calcium chloride CaCl2, sodium nitrate NaNO3, and calcium sulfate CaSO4) or with polymer particles with strong water-absorbing properties (such as polyacrylamide and sodium polyacrylate). While these strategies improve the performance of NaCl to some extent, they fail to fundamentally enhance its hygroscopicity and often only bring about minor improvements, making it difficult to significantly improve its catalytic effect in practical applications. Therefore, overcoming this bottleneck and improving the hygroscopic performance of NaCl in low-humidity environments remains an important research topic in artificial rainmaking catalysts. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a warm cloud catalyst and its preparation method to solve at least one of the problems of poor hygroscopicity, poor catalytic performance, low dispersion performance, and high relative humidity at which hygroscopicity begins in warm cloud catalysts prepared by existing methods.

[0007] In a first aspect, the present invention provides a method for preparing a warm cloud catalyst, comprising the following steps:

[0008] (1) Add the surfactant to the organic solvent, then add the co-surfactant, stir, and a transparent solution is obtained;

[0009] (2) Add water, silicon source, and catalyst to the transparent solution to react and obtain SiO2 nanomaterials. Add sodium dodecyl sulfate (SDS) to the SiO2 nanomaterials, sonicate, wash, and dry to obtain SDS-coated SiO2 nanoparticles.

[0010] (3) The SDS-coated SiO2 nanoparticles are added to a poor solvent to obtain a poor solvent-SiO2 phase, and NaCl is dissolved in water to obtain a NaCl solution.

[0011] (4) The poor solvent-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 7:3-9:1, precipitated, and filtered to obtain the warm cloud catalyst.

[0012] Furthermore, in step (1), the organic solvent is n-hexane or cyclohexane;

[0013] The surfactants mentioned include one or more of nonionic surfactants, cationic surfactants, or anionic surfactants;

[0014] The co-surfactant includes alcohols.

[0015] Furthermore, the nonionic surfactant includes one or more of Triton X-100, alkyl polyoxyethylene ether, and glycerol ester;

[0016] The cationic surfactant includes one or more of cetyltrimethylammonium bromide, cationic panthenol, and cationic silicone oil;

[0017] The anionic surfactants include one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium fatty alcohol ether sulfate.

[0018] Furthermore, in step (1), the volume ratio of organic solvent, surfactant and co-surfactant is 50-100:10-30:5-20.

[0019] Furthermore, in step (2), the silicon source is one or more of tetramethylsilane, tetraethyl silicate, or sodium silicate; and the catalyst is an acid or a base.

[0020] Furthermore, in step (2), the reaction temperature is 35-45℃ and the reaction time is 4-24h.

[0021] Furthermore, in step (2), the particle size of the SiO2 nanomaterial is 30-500 nm.

[0022] Furthermore, in step (3), the concentration of the SDS-coated SiO2 nanoparticles in the unsuitable solvent is 10–100 mg / mL, and the concentration of the NaCl solution is 0.5–3 mol / L.

[0023] Furthermore, in step (3), the undesirable solvent is one or more of ethanol, isopropanol, cyclohexane or acetone.

[0024] Secondly, the present invention provides a warm cloud catalyst prepared by the above method, wherein the warm cloud catalyst is a layer of SiO2 nanoparticles with hydroxyl groups coated on the surface of NaCl, and the central particle size of the warm cloud catalyst is 1-5 μm.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] (1) The warm cloud catalyst prepared by the method of the present invention is a single-layer coated SiO2 structure formed by NaCl core, and the surface of the prepared SiO2 nanomaterial contains hydroxyl groups (-OH), which can form hydrogen bonds with water, thereby making it easier to adsorb water vapor, forming local high humidity on the NaCl surface, and promoting the growth of NaCl moisture absorption.

[0027] (2) The SiO2 particles prepared by the method of the present invention form a relatively loose coating structure with NaCl. This structure can greatly increase the specific surface area of ​​the warm cloud artificial weather modification catalyst and facilitate the transport of water vapor molecules along the pores between SiO2 nanoparticles to the interior, thereby accelerating the hygroscopic growth of NaCl.

[0028] (3) The NaCl-SiO2 core-shell material obtained by the method of the present invention has the advantages of simple and convenient preparation process, low cost and low environmental hazard. It has been confirmed by hygroscopicity test, cloud chamber test and dynamic water vapor adsorption test that it has excellent warm cloud artificial rain catalyst activity.

[0029] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained through the details specifically pointed out in the description and drawings. Attached Figure Description

[0030] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0031] Figure 1 This is a schematic diagram of a cloud chamber and testing device in Experimental Example 2 of the present invention;

[0032] Figure 2 This is a graph showing the change in median particle size of cloud chamber droplets over time in Experiment Example 2 of this invention;

[0033] Figure 3 The diagram shows the water vapor adsorption volume of the warm cloud catalyst and pure NaCl prepared in Examples 1-3 of Experimental Example 2 of this invention under different relative humidities.

[0034] Figure 4 This is a number concentration diagram of the warm cloud catalyst and pure NaCl prepared in Example 1 of Experiment 2 of the present invention before the humidity reaches supersaturation. Detailed Implementation

[0035] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0036] A specific embodiment of the present invention discloses a method for preparing a warm cloud catalyst, comprising the following steps:

[0037] (1) Add the surfactant to the organic solvent, stir until homogeneous, then add the co-surfactant and stir until the solution is clear and transparent to obtain a transparent solution;

[0038] (2) Add water to the transparent solution, stir, add silicon source, add catalyst, and react to obtain SiO2 nanomaterials. Add sodium dodecyl sulfate (SDS) to the SiO2 nanomaterials, sonicate, wash, and dry to obtain SDS-coated SiO2 nanoparticles.

[0039] (3) The SDS-coated SiO2 nanoparticles are added to a poor solvent to obtain a poor solvent-SiO2 phase, and NaCl is dissolved in water to obtain a NaCl solution.

[0040] (4) The poor solvent-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 7:3-9:1, precipitated, filtered, and the warm cloud catalyst (i.e. NaCl-SiO2 micron particles) is obtained.

[0041] The SiO2 particles prepared by the method of this invention form a relatively loose coating structure with NaCl. This structure can significantly increase the specific surface area of ​​the warm cloud artificial weather modification catalyst and facilitate the transport of water vapor molecules along the pores between SiO2 nanoparticles, thereby accelerating the hygroscopic growth of NaCl. Furthermore, the SiO2 nanoparticles of this invention have hydroxyl groups (-OH) on their surface, thus further enhancing hydrophilicity. However, their larger molecular structure limits their solubility in water, thus allowing them to possess surfactant properties. In water droplets, the main molecular interaction between H2O molecules is hydrogen bonding. These bonds result in abnormally high surface tension, which is unfavorable for droplet formation and growth. The SiO2 particles of this invention, by forming weaker hydrogen bonds with water and accumulating on the droplet surface, weaken the hydrogen bonding forces between water molecules by not forming significant hydrogen bonds with water, thereby reducing the surface tension of the droplets. This facilitates further hygroscopic growth of the droplets into larger droplets, promoting the collision-merging growth process in warm cloud raindrops, and ultimately disrupting the metastable state of water droplets in the cloud, thus promoting rainfall.

[0042] Specifically, in step (1), the organic solvent is n-hexane or cyclohexane;

[0043] The surfactants mentioned include one or more of nonionic surfactants, cationic surfactants, or anionic surfactants;

[0044] The co-surfactant includes alcohols, preferably n-butanol and / or n-pentanol;

[0045] Preferably, the nonionic surfactant includes one or more of Triton X-100, alkyl polyoxyethylene ether, and glycerol ester;

[0046] The cationic surfactant includes one or more of cetyltrimethylammonium bromide, cationic panthenol, and cationic silicone oil;

[0047] The anionic surfactants include one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium fatty alcohol ether sulfate.

[0048] Specifically, in step (1), the volume ratio of organic solvent, surfactant and co-surfactant is 50-100 (e.g., 60, 70, 80, 90): 10-30 (e.g., 12, 14, 16, 18, 20, 22, 24, 26, 28): 5-20 (e.g., 7, 9, 11, 13, 15, 17, 19).

[0049] It should be noted that organic solvents can cause NaCl to precipitate from the solution phase, making them undesirable solvent phases in antisolvent precipitation methods. They play an important role in the formation of NaCl micron crystals, but at low concentrations, they can inhibit NaCl precipitation. Surfactants and co-surfactants promote the formation of SiO2 and NaCl coating structures, but at low concentrations, they are less likely to achieve this effect. Due to the low solubility of surfactants and co-surfactants, at higher concentrations, they are difficult to completely dissolve, resulting in more impurities in the product.

[0050] Preferably, in step (1), the mixture is stirred for 10-30 minutes (e.g., 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes) until homogeneous, and then stirred for 10-30 minutes (e.g., 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes) until the solution is clear and transparent.

[0051] Specifically, in step (2), the water is ultrapure water or deionized water;

[0052] The silicon source is one or more of tetramethylsilane (TMOS), tetraethyl silicate (TEOS), or sodium silicate;

[0053] The catalyst is an acid or a base, preferably hydrochloric acid or ammonia. The catalyst adjusts the pH of the solution to neutral, preferably 6.5 to 7.5.

[0054] Specifically, in step (2), the volume ratio of water to the co-surfactant in step (1) is 2-10 (e.g., 3, 4, 5, 6, 7, 8, 9): 5-20 (e.g., 7, 9, 11, 13, 15, 17, 19), and the volume ratio of water to silicon source is 2-10 (e.g., 3, 4, 5, 6, 7, 8, 9): 2-10 (e.g., 3, 4, 5, 6, 7, 8, 9).

[0055] It should be noted that a low water content allows for slow hydrolysis of the silicon source. Excessive water content causes the silicon source to rapidly hydrolyze into SiO2, resulting in uncontrollable particle size and a wide distribution range of the prepared SiO2. Adjusting the water content within a relatively low range allows for control of the synthesized SiO2 particle size, enabling the study of the impact of different SiO2 particle sizes on material properties. Preferably, the silicon source is added after stirring for 10–30 minutes.

[0056] Specifically, in step (2), the reaction temperature is 35-45℃, for example, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, and the reaction time is 4-24h, for example, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h.

[0057] It should be noted that different reaction temperatures and reaction times can control the particle size distribution of the generated SiO2. Generally, higher reaction temperatures and longer reaction times can reduce the particle size of the generated SiO2.

[0058] Specifically, in step (2), the particle size of the SiO2 nanomaterial is 30-500nm, for example, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm.

[0059] Specifically, in step (2), the mass-to-volume ratio of the SiO2 nanomaterial to sodium dodecyl sulfate is 8-10g (e.g., 8.2g, 8.4g, 8.6g, 8.8g, 9.0g, 9.2g, 9.4g, 9.6g, 9.8g): 0.5-1mL (e.g., 0.6mL, 0.7mL, 0.8mL, 0.9mL).

[0060] It should be noted that the addition of sodium dodecyl sulfate can improve the dispersibility of SiO2 and promote its coating effect on NaCl. However, if the sodium dodecyl sulfate content is too high, SiO2 will be suspended in the solution, resulting in poor coating effect.

[0061] Specifically, in step (2), the ultrasonic time is 1-2 hours, for example, 1.2 hours, 1.4 hours, 1.6 hours, or 1.8 hours. The particles are first washed with ethanol 3-4 times, then washed with ultrapure water 3-4 times, and dried at a temperature of 50-70°C, for example, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, or 68°C, and a pressure of 0.05-0.08 MPa (for example, 0.055 MPa, 0.06 MPa, 0.065 MPa, 0.070 MPa, or 0.075 MPa) for 10-12 hours (for example, 10.2 hours, 10.4 hours, 10.6 hours, 10.8 hours, 11.0 hours, 11.2 hours, 11.4 hours, 11.6 hours, or 11.8 hours) to obtain SDS-coated SiO2 nanoparticles.

[0062] Specifically, in step (3), the undesirable solvent is one or more of ethanol, isopropanol, cyclohexane or acetone.

[0063] Specifically, in step (3), the concentration of the SDS-coated SiO2 nanoparticles in the unsuitable solvent is 10-100 mg / mL, for example, 20 mg / mL, 30 mg / mL, 40 mg / mL, 50 mg / mL, 60 mg / mL, 70 mg / mL, 80 mg / mL, 90 mg / mL, and the concentration of the NaCl solution is 0.5-3 mol / L, 0.7 mg / mL, 0.9 mg / mL, 1.1 mg / mL, 1.3 mg / mL, 1.5 mg / mL, 1.7 mg / mL, 1.9 mg / mL, 2.1 mg / mL, 2.3 mg / mL, 2.5 mg / mL, 2.7 mg / mL, 2.9 mg / mL.

[0064] It should be noted that within the above concentration range, a good SiO2 monolayer coating structure can be formed on NaCl. When the relative concentration of NaCl is high, the coating will be incomplete, resulting in a decrease in hygroscopicity and warm cloud catalytic ability. When the relative concentration of NaCl is high, an over-coated structure will be formed, and the outer SiO2 layer will easily fall off or form clusters, resulting in a decrease in the warm cloud catalytic performance of the material.

[0065] Specifically, in step (4), the total flow rate of the poor solvent-SiO2 phase and NaCl solution is 1 to 10 mL / min, for example, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL.

[0066] When the flow rate is set within this range, the particle size of the prepared NaCl-SiO2 crystals falls within the 1-10 micrometer range required for the warm cloud catalyst. If the flow rate is too low, the resulting NaCl-SiO2 crystals will be too large, while if the flow rate is too high, the resulting NaCl-SiO2 crystals will be too small and have an excessively wide particle size distribution, thus reducing the warm cloud catalytic performance of the material.

[0067] Specifically, in step (4), the filtrate is obtained by filtration, and the filtrate is distilled under reduced pressure to obtain a poor solvent and water, which can be returned to step (3) for recycling.

[0068] It should be noted that in step (4), the flow rate ratio of the poor solvent-SiO2 phase and NaCl solution is controlled within the range of the present invention. This is because if the flow rate is below this range, the proportion of NaCl in the resulting product will be too high, making it difficult to achieve complete coating of NaCl by SiO2, resulting in a decrease in the hygroscopicity and catalytic activity of the material. If the flow rate is above this range, SiO2 is prone to self-aggregation, that is, some SiO2 nanoparticles are not coated on NaCl, but form SiO2 clusters, resulting in a decrease in the overall hygroscopicity of the product and a waste of materials.

[0069] The antisolvent precipitation method works by first dissolving NaCl in a good solvent and then introducing it into a large amount of poor solvent, where NaCl crystals immediately precipitate. However, conventional antisolvent precipitation methods often have drawbacks such as excessive solvent consumption, low crystal yield, and high time costs. This invention uses a continuous flow device to generate crystal precipitation to prepare micron-sized NaCl-SiO2 crystals, and the poor solvent can be recycled, saving costs.

[0070] The NaCl-SiO2 core-shell material obtained by the method of this invention has the advantages of simple and convenient preparation process, low cost, and low environmental hazard. Furthermore, its excellent warm cloud artificial rainmaking catalyst activity has been confirmed through hygroscopicity experiments, cloud chamber experiments, and dynamic water vapor adsorption experiments.

[0071] Another specific embodiment of the present invention discloses a warm cloud catalyst prepared by the above method, wherein the warm cloud catalyst is a layer of SiO2 nanoparticles with hydroxyl groups coated on the surface of NaCl.

[0072] Specifically, the central particle size of the warm cloud catalyst is 1-5 μm, for example, 2 μm, 3 μm, 4 μm.

[0073] Compared with existing technologies, the warm cloud catalyst prepared by the method of this invention is a monolayer SiO2 structure formed by NaCl cores. Furthermore, the surface of the prepared SiO2 nanomaterials contains hydroxyl groups (-OH), which can form hydrogen bonds with water, thus more easily adsorbing water vapor and creating localized high humidity on the NaCl surface, promoting the hygroscopic growth of NaCl. Moreover, the particle size of the NaCl all meet the requirements of 1-10 μm for warm cloud weather modification catalyst materials, which is the foundation for its use as a good warm cloud weather modification catalyst.

[0074] The SiO2 nanomaterials prepared by the method of the present invention have a particle size of 30-500 nm, the central particle size of the warm cloud catalyst is 1-5 μm, the coating thickness is 40-370 nm, and the relative humidity at which the warm cloud catalyst begins to absorb moisture is 20-45%, and the relative humidity at which it completely deliquesces is 67-70.5%.

[0075] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0076] Example 1

[0077] The preparation method of a warm cloud catalyst in this embodiment includes the following steps:

[0078] (1) Add 0.1g Triton X-100 to 75mL n-hexane, stir for 20min, then add 12.5mL n-butanol, stir for 20min until the solution is clear and transparent, and obtain a transparent solution;

[0079] (2) Add 6 mL of ultrapure water to the transparent solution, stir for 20 min, add 8 mL of LTEOS, and then add ammonia to adjust the pH value to 6.5-7.5. React at 40 °C for 12 h to obtain SiO2 nanomaterials. Add 5 g of the SiO2 nanomaterials and 0.1 g of sodium dodecyl sulfate (SDS) to 10 mL of ultrapure water, sonicate for 2 h, filter, wash with ethanol 3 times, wash with ultrapure water 3 times, and dry at 60 °C and 0.08 MPa for 12 h to obtain SDS-coated SiO2 nanoparticles.

[0080] (3) The SDS-coated SiO2 nanoparticles were added to ethanol to obtain an ethanol-SiO2 phase. The concentration of the SDS-coated SiO2 nanoparticles in ethanol was 55 mg / mL. NaCl was dissolved in water to obtain a NaCl solution with a concentration of 1.75 mol / L.

[0081] (4) The ethanol-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 5:1, and the total flow rate of the ethanol-SiO2 phase and NaCl solution is 2 mL / min. After mixing, precipitation, and filtration, the warm cloud catalyst (i.e., NaCl-SiO2 micron particles) is obtained.

[0082] Example 2

[0083] The preparation method of a warm cloud catalyst in this embodiment includes the following steps:

[0084] (1) Add 0.1g of hexadecyltrimethylammonium bromide to 50mL of cyclohexane and stir for 10min until the solution is clear and transparent to obtain a transparent solution;

[0085] (2) Add 2 mL of ultrapure water to the transparent solution, stir for 10 min, add 8 mL of LTMOS, and then add ammonia to adjust the pH to 6.5-7.5. React at 35 °C for 24 h to obtain SiO2 nanomaterials. Add 5 g of the SiO2 nanomaterials and 0.1 g of sodium dodecyl sulfate (SDS) to 10 mL of ultrapure water, sonicate for 1 h, filter, wash 4 times with ethanol, then wash 4 times with ultrapure water, and dry at 50 °C and 0.05 MPa for 10 h to obtain SDS-coated SiO2 nanoparticles.

[0086] (3) The SDS-coated SiO2 nanoparticles are added to isopropanol to obtain an isopropanol-SiO2 phase. The concentration of the SDS-coated SiO2 nanoparticles in isopropanol is 10 mg / mL. NaCl is dissolved in water to obtain a NaCl solution with a concentration of 0.5 mol / L.

[0087] (4) The isopropanol-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 7:3, and the total flow rate of the isopropanol-SiO2 phase and NaCl solution is 6 mL / min. After mixing, precipitation, and filtration, the warm cloud catalyst (i.e., NaCl-SiO2 micron particles) is obtained.

[0088] Example 3

[0089] The preparation method of a warm cloud catalyst in this embodiment includes the following steps:

[0090] (1) Add 0.1g sodium dodecylbenzenesulfonate to 100mL n-hexane, stir for 30min, then add 20mL n-butanol, stir for 30min until the solution is clear and transparent, and obtain a transparent solution;

[0091] (2) Add 10 mL of ultrapure water to the transparent solution, stir for 20 min, add 10 mL of sodium silicate, and then add ammonia to adjust the pH to 6.5-7.5. React at 45 °C for 4 h to obtain SiO2 nanomaterials. Add 5 g of the SiO2 nanomaterials and 0.1 g of sodium dodecyl sulfate (SDS) to 10 mL of ultrapure water, sonicate for 1.5 h, filter, wash three times with ethanol, then wash three times with ultrapure water, and dry at 70 °C and 0.075 MPa for 11 h to obtain SDS-coated SiO2 nanoparticles.

[0092] (3) The SDS-coated SiO2 nanoparticles were added to cyclohexane to obtain a cyclohexane-SiO2 phase. The concentration of the SDS-coated SiO2 nanoparticles in cyclohexane was 100 mg / mL. NaCl was dissolved in water to obtain a NaCl solution with a concentration of 1.75 mol / L.

[0093] (4) The cyclohexane-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 9:1, and the total flow rate of the cyclohexane-SiO2 phase and NaCl solution is 10 mL / min. After mixing, precipitation, and filtration, the warm cloud catalyst (i.e., NaCl-SiO2 micron particles) is obtained.

[0094] Comparative Example 1

[0095] The preparation method of the warm cloud catalyst in this comparative example is the same as that in Example 1, except that the SDS-coated SiO2 nanoparticles in step (3) are replaced with the SiO2 nanomaterials in step (2).

[0096] Comparative Example 2

[0097] The preparation method of the warm cloud catalyst in this comparative example is the same as that in Example 1, except that the reaction temperature in step (2) is 25°C.

[0098] Comparative Example 3

[0099] The preparation method of the warm cloud catalyst in this comparative example is the same as that in Example 1, except that the reaction temperature in step (2) is 45°C.

[0100] Comparative Example 4

[0101] The preparation method of the warm cloud catalyst in this comparative example is the same as that in Example 1, except that in step (4), the ethanol-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 2:1.

[0102] Comparative Example 5

[0103] The preparation method of the warm cloud catalyst in this comparative example is the same as that in Example 1, except that in step (4), the ethanol-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 10:1.

[0104] Comparative Example 6

[0105] The preparation method of the warm cloud catalyst in this comparative example is the same as that in Example 1, except that in step (1), the amount of n-hexane is 40 mL.

[0106] Experimental Example 1

[0107] (a) Warm cloud catalysts were prepared according to the methods of Examples 1-3 and Comparative Examples 1-6, respectively. The particle size of the SiO2 nanomaterials obtained in step (2) and the center particle size of the warm cloud catalysts obtained in step (4) were tested, as well as the thickness of the SiO2 nanoparticles with hydroxyl groups, i.e., the coating thickness. The results are shown in Table 1.

[0108] Among them, the center particle size test is the particle size distribution measured by an aerodynamic particle size spectrometer (APS) when the catalyst material is dispersed in an 800L smoke chamber, and the coating thickness is tested by a transmission electron microscope (TEM).

[0109] Table 1

[0110]

[0111]

[0112] (2) Moisture absorption performance test

[0113] The hygroscopicity of the material of this invention was tested using a dynamic water vapor adsorption instrument.

[0114] The hygroscopic properties of the catalysts prepared in Examples 1-3 and Comparative Examples 1-6 were tested, and the results are shown in Table 2.

[0115] Table 2

[0116] Group Relative humidity at which moisture absorption begins / % Relative humidity at complete deliquescence / % Example 1 21.5 67.3 Example 2 36.8 69.3 Example 3 42.1 70.4 Comparative Example 1 60.5 74.1 Comparative Example 2 58.3 72.2 Comparative Example 3 64.2 73.5 Comparative Example 4 63.0 71.0 Comparative Example 5 67.6 72.3 Comparative Example 6 71.2 74.3

[0117] According to Tables 1 and 2, in Comparative Example 1, since the SiO2 nanoparticles were not coated with SDS, their coating ability for NaCl was reduced. Although the particle size of the SiO2 nanoparticles was not changed compared with Example 1, the central particle size and coating layer thickness of the Nuanyun catalyst were reduced, indicating that the synthesized Nuanyun catalyst material was not successfully coated.

[0118] In Comparative Example 2, the SiO2 nanoparticles were synthesized at too low a temperature, resulting in a low particle size. Although they could form a monolayer coating, the small SiO2 nanoparticles had poor moisture absorption capacity, and the prepared warm cloud catalyst had poor performance.

[0119] In Comparative Example 3, the high temperature during the synthesis of SiO2 nanoparticles resulted in excessively large particle sizes. The large SiO2 nanoparticles had poor coating performance and were difficult to form a single-layer coating structure, which reduced the performance of the warm cloud catalyst.

[0120] In Comparative Example 4, the flow rate ratio of ethanol-SiO2 phase was too low, that is, the proportion of SiO2 nanoparticles in the obtained product was low, resulting in incomplete coating and a smaller measured coating thickness, thus the prepared Nuanyun catalyst had poor effect.

[0121] In Comparative Example 5, the flow rate ratio of ethanol-SiO2 phase was too high, that is, the proportion of SiO2 nanoparticles in the obtained product was too high, resulting in an excessively thick coating layer, which was not a single-layer coating, and the central particle size was too large, resulting in poor moisture absorption performance of the material.

[0122] In Comparative Example 6, the amount of n-hexane added was too low, resulting in small particle size of the synthesized SiO2 nanoparticles and poor coating ability, leading to a low coating layer thickness and poor moisture absorption effect of the prepared Nuanyun catalyst.

[0123] Experimental Example 2

[0124] The warm cloud catalyst prepared in Example 1 was used to simulate a catalytic precipitation process under warm cloud conditions in the Beijing aerosol and cloud interaction chamber (BACIC) at the Beijing Artificial Weather Modification Scientific Experiment Base. The BACIC chamber was 70m thick. 3 Cloud room diagram as shown Figure 1 As shown.

[0125] The volume of the cloud chamber for aerosol-cloud interaction in Beijing is 70m. 3 The cloud chamber can be approximated as a cylinder with a diameter of 2.6m and a height of 14m. The controllable temperature range is -45℃ to room temperature, and the controllable pressure range is 1hPa to atmospheric pressure. It simulates the actual cloud environment by expanding into a cloud. The cloud chamber is equipped with a 3772 particle counter (CPC), a 3938 scanning electromobility particle size spectrometer (SMPS), and a 3321 aerodynamic particle size spectrometer (APS) manufactured by TSI Corporation (USA) to measure the aerosol number concentration spectrum of particles with a diameter of 0.5-20μm. These instruments are used to measure the aerosol number concentration of particles larger than 3nm, the aerosol number concentration spectrum of particles with a diameter of 0.02-0.7μm, and the aerosol number concentration spectrum of particles with a diameter of 0.5-20μm, respectively, achieving a wide range of aerosol number spectrum measurements from small to large particle sizes before expanding into a cloud. After adiabatic expansion into clouds, the pressure inside the cloud chamber decreases, and the particle size spectrometer cannot work properly when the pressure is below the standard atmospheric pressure. Therefore, the warm cloud artificial weather modification catalyst after cloud formation acts as a condensation nucleus and undergoes a hygroscopic growth process. The FM-120 fog droplet spectrometer is needed to measure the raindrop particle size in the range of 2-50μm.

[0126] like Figure 2 By comparing the median aerodynamic diameter (MVD) of the droplets in the cloud chamber experiment, it can be clearly seen that the median diameter of the water droplets produced by the NaCl-SiO2 warm cloud catalyst prepared in Example 1 is about 45 μm, while the median diameter of the water droplets formed by pure NaCl is only about 30 μm. That is, the NaCl-SiO2 material has stronger catalytic warm cloud artificial rainmaking performance.

[0127] like Figure 4 Based on cloud chamber CPC data, when 0.5g of NaCl and 0.5g of NaCl-SiO2 material prepared in Example 1 were added in the same amount, the number concentration of the NaCl-SiO2 warm cloud weather modification catalyst before the humidity reached supersaturation was approximately 230 ions / cm³. 3 The number concentration of pure NaCl is only 70 ions / cm³. 3 This indicates that the NaCl-SiO2 weather modification catalyst material has better dispersibility, which is related to the fact that the SiO2 surface coating separates the NaCl micron particles, reducing the electrostatic effect between them.

[0128] The water vapor adsorption volumes of pure NaCl and NaCl-SiO2 prepared in Examples 1-3 under different relative humidities are as follows: Figure 3As shown, NaCl-SiO2 material exhibits strong water vapor adsorption capacity even at low relative humidity. Furthermore, compared to pure NaCl which begins to deliquesce at 75% RH, NaCl-SiO2 material deliquesces earlier at 68%–71% RH. This earlier deliquescenic process allows the corresponding warm cloud catalyst material to initiate collision and growth processes earlier, thereby improving catalytic efficiency and making it suitable for more cloud types.

[0129] The inventors also conducted the above experiments on catalysts prepared in other embodiments, and the results were basically the same. Due to space limitations, they will not be listed one by one.

[0130] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a warm cloud catalyst, characterized in that, Includes the following steps: (1) Add the surfactant to the organic solvent, then add the co-surfactant, stir, and obtain a transparent solution; (2) Add water, silicon source, and catalyst to the transparent solution to react and obtain SiO2 nanomaterials. Add sodium dodecyl sulfate to the SiO2 nanomaterials, sonicate, wash, and dry to obtain SDS-coated SiO2 nanoparticles. (3) The SDS-coated SiO2 nanoparticles are added to a poor solvent to obtain a poor solvent-SiO2 phase; NaCl is dissolved in water to obtain a NaCl solution; (4) The poor solvent-SiO2 phase and NaCl solution are mixed at a flow rate ratio of 7:3-9:1, precipitated, and filtered to obtain the warm cloud catalyst; In step (1), the surfactant includes one or more of nonionic surfactants, cationic surfactants or anionic surfactants; The nonionic surfactants mentioned include one or more of Triton X-100, alkyl polyoxyethylene ethers, and glycerol esters; The cationic surfactant includes one or more of cetyltrimethylammonium bromide, cationic panthenol, and cationic silicone oil; The anionic surfactants include one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium fatty alcohol ether sulfate; The co-surfactant is n-butanol and / or n-pentanol.

2. The method for preparing a warm cloud catalyst according to claim 1, characterized in that, In step (1), the organic solvent is n-hexane or cyclohexane.

3. The method for preparing a warm cloud catalyst according to claim 1 or 2, characterized in that, In step (1), the volume ratio of organic solvent, surfactant and co-surfactant is 50~100:10~30:5~20.

4. The method for preparing a warm cloud catalyst according to claim 1 or 2, characterized in that, In step (2), the silicon source is one or more of tetramethylsilane, tetraethyl silicate, or sodium silicate; the catalyst is an acid or a base.

5. The method for preparing a warm cloud catalyst according to claim 1, characterized in that, In step (2), the reaction temperature is 35-45℃ and the reaction time is 4-24h.

6. The method for preparing a warm cloud catalyst according to claim 1, characterized in that, In step (2), the particle size of the SiO2 nanomaterial is 30-500 nm.

7. The method for preparing a warm cloud catalyst according to claim 1, characterized in that, In step (3), the concentration of the SDS-coated SiO2 nanoparticles in the unsuitable solvent is 10~100 mg / mL, and the concentration of the NaCl solution is 0.5~3 mol / L.

8. The method for preparing a warm cloud catalyst according to claim 1, characterized in that, In step (3), the undesirable solvent is one or more of ethanol, isopropanol, cyclohexane or acetone.

9. A warm cloud catalyst prepared by any one of claims 1-8, characterized in that, The warm cloud catalyst is a SiO2 nanoparticle with hydroxyl groups coated on the surface of NaCl, and the central particle size of the warm cloud catalyst is 1-5 μm.

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