Warm cloud catalyst and preparation method thereof

Abstract

The invention relates to a warm cloud catalyst and a preparation method thereof, belongs to the technical field of artificial influence weather catalysts, and is used for solving at least one of the problems of poor hygroscopicity, poor catalytic performance, low dispersing performance, high relative humidity of initial moisture absorption and the like of the warm cloud catalyst prepared by the existing method. The warm cloud catalyst prepared by the method disclosed by the invention is of a single-layer coated SiO2 structure formed by a NaCl core, and the surface of the prepared SiO2 nano material contains hydroxyl (-OH) which can form hydrogen bonds with water, so that water vapor is more easily adsorbed, local high humidity is formed on the surface of NaCl, and the moisture absorption growth of NaCl is promoted. And the particle size of NaCl meets the range of 1-10 [mu] m required by a warm-cloud weather-modifying catalyst material, which is the basis of a good warm-cloud weather-modifying catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial weather modification catalysts, and particularly to a warm cloud catalyst and a preparation method thereof. Background Art

[0002] Under the background of global climate change, the increase in greenhouse gas emissions has led to global warming, frequent climate anomalies, intensified uneven precipitation distribution, and an increase in extreme weather events, which have a greater impact on people's livelihood and social harmony. In addition, there are also problems such as the increasingly serious global water shortage, uneven distribution of fresh water resources, prominent regional water shortage problems, and intensified water resource supply-demand contradictions in the water resources field, posing severe challenges to the agricultural production field and urban water supply, such as water shortage during the wheat growing season, tight cotton irrigation water, severe water shortage, seasonal water shortage, etc.

[0003] Water vapor in the atmosphere, as a natural resource, is equivalent to about 10% of the fresh water in all rivers and lakes on the earth. Using artificial weather modification catalysts as cloud condensation nuclei (CCN) is an effective method to accelerate the formation of water droplets and then collect water vapor in the atmosphere through rainfall. Therefore, artificial rainfall enhancement operations have important practical significance in fields such as ensuring precipitation for agricultural production, maintaining good weather conditions for large international events, and preventing extreme weather. Currently, in the field of artificial weather modification catalysts, there are mainly three categories: refrigerants, artificial ice nuclei, and hygroscopic nuclei. Refrigerants sublimate or vaporize in the cloud layer by themselves, and during this process, they absorb heat, greatly reducing the temperature of the surrounding air, making the air humidity reach the supersaturated state, thereby promoting the sublimation of water vapor to form ice crystals. At the same time, it destroys the metastable state of supercooled water droplets in the cloud, triggering their spontaneous nucleation and freezing, and activating the natural ice nuclei existing in the cloud into ice. Commonly used refrigerants include dry ice (solid CO 2 ), liquid carbon dioxide (LC), liquid nitrogen (LN), liquid propane (LP), etc. Artificial ice nuclei are artificial weather modification catalysts for cold clouds, that is, clouds with a temperature below 0°C. Currently, the most widely used artificial ice nuclei are silver iodide (AgI) and modified doped materials based on AgI. The main reason why AgI can exert ice nucleus activity is that its hexagonal crystal lattice structure is extremely similar to that of ice crystals, making it easier for ice crystals to form on its surface, thereby catalyzing the cold cloud precipitation process. For hygroscopic nuclei, they are generally applied to warm clouds, that is, clouds with a temperature higher than 0°C. Hygroscopic nuclei can adsorb water vapor in warm clouds and finally completely transform into water droplets, and the formed water droplets grow continuously through the processes of collision and aggregation until the water droplets become large enough to fall like rain. Commonly used materials for warm cloud catalysis include sodium chloride (NaCl), calcium chloride (CaCl 2 ), urea (NH 2 CONH 2) and ammonium nitrate (NH 4 NO 3 )wait.

[0004] Sodium chloride (NaCl), as a typical water-soluble hygroscopic warm cloud seeding material, has been used in the field of artificial weather modification for decades. Its superior performance and low cost make it an important material in research and practical applications. Compared with cold cloud seeding materials, the application of NaCl in warm clouds shows a wider applicability. For example, although dry ice can play a role as a refrigerant in the process of artificial rainfall, its high cost and potential harm to the environment as a greenhouse gas make it incompatible with the requirements of green and sustainable development. In addition, artificial ice nucleus materials (such as silver iodide AgI) are still controversial in environmental risk assessment. AgI may release silver nanoparticles and iodine during decomposition, which have strong toxic effects on human health and ecosystems, and their large-scale use will lead to excessive costs.

[0005] Therefore, how to choose a seeding material that is both efficient and environmentally friendly has become a hot topic of research. In addition to NaCl, some other warm cloud artificial weather modification catalyst materials have also been proposed in the exploration, such as zeolite, silica gel, metal organic frameworks (MOFs), etc. Although these materials have certain hygroscopic and catalytic properties, their water adsorption capacity is relatively low, and they also face the problems of high production costs and complex preparation processes. In addition, the water release characteristics of these materials are relatively significant, which further increases the limitations of their application. Therefore, the application of NaCl in the process of artificial rainfall is restricted by its hygroscopic properties, especially under environmental conditions where the relative humidity (RH) is below 75%, the hygroscopic properties of NaCl crystals are not significant, especially under conditions below 25% RH, there is almost no detectable water vapor adsorption. This limitation seriously affects the widespread application of NaCl as a warm cloud seeding material. In order to solve this problem, researchers have also tried a variety of methods to improve the hygroscopic properties of NaCl. For example, by mixing NaCl with other hygroscopic salts (such as calcium chloride (CaCl)) with other hygroscopic salts (such as calcium chloride (CaCl)), NaCl can be used as a seeding material for warm clouds. 2 、Sodium nitrate NaNO 3 Calcium sulfate CaSO 4 Although these strategies have improved the performance of NaCl to a certain extent, they still fail to fundamentally improve the hygroscopicity of NaCl, and often only bring about minor improvements, making it difficult to significantly improve its catalytic effect in practical applications. Therefore, how to break through this bottleneck and improve the hygroscopicity of NaCl in a low-humidity environment is still an important topic in the current research on artificial rain catalysts. Summary of the invention

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

[0007] In the first aspect, the present invention provides a preparation method of a warm cloud catalyst, including the following steps:

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

[0009] (2) Add water, a silicon source, and a catalyst to the transparent solution, and carry out a reaction to obtain SiO 2 nanomaterials. Add sodium dodecyl sulfate (SDS) to the SiO 2 nanomaterials, perform ultrasonic treatment, washing, and drying to obtain SDS-coated SiO 2 nanoparticles;

[0010] (3) Add the SDS-coated SiO 2 nanoparticles to a poor solvent to obtain a poor solvent-SiO 2 phase. Dissolve NaCl in water to obtain a NaCl solution;

[0011] (4) Mix the poor solvent-SiO 2 phase and the NaCl solution at a flow rate ratio of 7:3 - 9:1, precipitate, and filter to obtain the warm cloud catalyst.

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

[0013] The surfactant includes one or more of a non-ionic surfactant, a cationic surfactant, or an anionic surfactant;

[0014] The co-surfactant includes an alcohol.

[0015] Further, the non-ionic surfactant includes one or more of Triton X-100, alkyl polyoxyethylene ether, and glyceride;

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

[0017] The anionic surfactant includes one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and fatty alcohol ether sulfate.

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

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

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

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

[0022] Further, in step (3), the concentration of the SDS-coated SiO 2 nanoparticles in the poor solvent is 10-100 mg / mL, and the concentration of the NaCl solution is 0.5-3 mol / L.

[0023] Further, in step (3), the poor solvent is one or several of ethanol, isopropanol, cyclohexane or acetone.

[0024] In a second aspect, the present invention provides a warm cloud catalyst prepared by the above method, and the warm cloud catalyst is a layer of SiO with hydroxyl groups coated on the surface of NaCl 2 nanoparticles, and the central particle size of the warm cloud catalyst is 1-5 μm.

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

[0026] (1) The warm cloud catalyst prepared by the method of the present invention has a single-layer coating SiO 2 structure formed with a NaCl core, and the prepared SiO 2 nanomaterial surface contains hydroxyl groups (-OH), which can form hydrogen bonds with water, so it is easier to adsorb water vapor, form local high humidity on the NaCl surface, and promote the hygroscopic growth of NaCl;

[0027] (2) The SiO 2 with the particle size prepared by the method of the present invention forms a relatively loose coating structure with NaCl, and this structure can greatly increase the specific surface area of the warm cloud artificial weather modification catalyst and is conducive to the transmission of water vapor molecules along the pores between the SiO 2 nanoparticles to the inside, thereby accelerating the hygroscopic growth of NaCl;

[0028] (3) The NaCl-SiO obtained by the method of the present invention 2The core-shell material has the advantages of simple and convenient preparation process, low cost, and little environmental harm, and its excellent warm cloud artificial rainfall catalyst activity is confirmed by hygroscopicity experiments, cloud chamber experiments, dynamic water vapor adsorption experiments, etc.

[0029] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the following description, and some advantages can be made obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the content specifically pointed out in the description and the drawings. Description of the Drawings

[0030] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals represent the same components.

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

[0032] Figure 2 It is a graph showing the change of the median droplet size in the cloud chamber droplet size spectrum over time in Test Example 2 of the present invention;

[0033] Figure 3 It is a graph of the water vapor adsorption volume of the warm cloud catalysts prepared in Examples 1-3 and pure NaCl at different relative humidities in Test Example 2 of the present invention;

[0034] Figure 4 It is a graph of the number concentration of the warm cloud catalyst prepared in Example 1 and pure NaCl before the humidity reaches supersaturation in Test Example 2 of the present invention. Detailed Embodiments

[0035] The following will specifically describe the preferred embodiments of the present invention with reference to the drawings, where the drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

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

[0037] (1) Add a surfactant to an organic solvent, stir evenly, and then add a 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 a silicon source, and then add a catalyst, and carry out a reaction to obtain SiO 2 nano-material, and the SiO 2Sodium dodecyl sulfate (SDS) was added to the nanomaterials, followed by ultrasonic treatment, washing, and drying to obtain SDS-coated SiO 2 nanoparticles;

[0039] (3) The SDS-coated SiO 2 nanoparticles were added to a poor solvent to obtain a poor solvent-SiO 2 phase, and NaCl was dissolved in water to obtain an NaCl solution;

[0040] (4) The poor solvent-SiO 2 phase and the NaCl solution were mixed at a flow rate ratio of 7:3 - 9:1, followed by precipitation and filtration to obtain the warm cloud catalyst (i.e., NaCl-SiO 2 microparticles).

[0041] The SiO 2 prepared by the method of the present invention forms a relatively loose coating structure with NaCl. This structure can greatly increase the specific surface area of the warm cloud weather modification catalyst and is conducive to the transmission of water vapor molecules along the pores between the SiO 2 nanoparticles to the inside, thereby accelerating the hygroscopic growth of NaCl. In addition, the SiO 2 nanoparticles of the present invention have hydroxyl groups (-OH) on their surfaces. Therefore, the hydrophilicity is further improved, but its relatively large molecular structure limits its solubility in water, so it has the characteristics of a surfactant. In water droplets, the main molecular interaction between H 2 O is a hydrogen bond. These bonds result in an abnormally large surface tension of water, which is not conducive to the formation and growth of water droplets. However, the SiO 2 of the present invention forms weaker hydrogen bonds with water and enriches on the surface of water droplets. By not forming significant hydrogen bonds with water, the hydrogen bond force between water molecules is weakened, thereby reducing the surface tension of water droplets, which is conducive to the further hygroscopic growth of water droplets into large droplets, promoting the collision - coalescence growth process in warm cloud raindrops, and further destroying the metastable state of water droplets in the cloud, thus promoting the occurrence of rainfall.

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

[0043] The surfactant includes one or more of non-ionic surfactants, cationic surfactants, or anionic surfactants;

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

[0045] Preferably, the non-ionic surfactant includes one or more of Triton X-100, alkyl polyoxyethylene ether, and glyceride;

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

[0047] The anionic surfactant includes one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and fatty alcohol ether sulfate.

[0048] Specifically, in step (1), the volume ratio of the 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 the organic solvent can precipitate NaCl from the solution phase and is the poor solvent phase in the anti-solvent precipitation method, which plays an important role in the formation of NaCl micron crystals. When the content is low, the precipitation of NaCl will be inhibited; the role of the surfactant and co-surfactant is to promote the formation of the SiO 2 coated structure with NaCl. When the content is low, it is difficult to play the above role. Due to the low solubility of the surfactant and co-surfactant, when the content is high, it is difficult to completely dissolve, resulting in more impurities in the product.

[0050] Preferably, in step (1), stir for 10-30 min (e.g., 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min) until uniform, and stir for 10-30 min (e.g., 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min) 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 orthosilicate (TEOS), or sodium silicate;

[0053] The catalyst is an acid or a base. Preferably, the acid is hydrochloric acid and the base is ammonia water. The catalyst adjusts the pH value of the solution to neutral, and the preferred pH value is 6.5-7.5.

[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 the 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 when the content of water is relatively small, the silicon source is hydrolyzed slowly. When the water content is too high, the silicon source is rapidly hydrolyzed into SiO 2 resulting in difficulty in controlling the particle size of the prepared SiO 2 and a wide distribution range; adjustment within a relatively small range of water can control the particle size of the synthesized SiO 2 to study the influence of SiO with different particle sizes 2 on the material properties. Preferably, stir for 10-30 min and then add the silicon source.

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

[0057] It should be noted that different reaction temperatures and reaction times can control the particle size distribution of the generated SiO 2 Generally, a higher reaction temperature and a longer reaction time can reduce the particle size of the generated SiO 2 particle size.

[0058] Specifically, in step (2), the particle size of the SiO 2 nanomaterials is 30-500 nm, e.g., 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm.

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

[0060] It should be noted that the addition of sodium dodecyl sulfate can improve the dispersion of SiO 2 and promote its coating effect on NaCl. However, when the content of sodium dodecyl sulfate is too high, it will cause SiO2 It is in a suspended state in the solution, resulting in a poor coating effect.

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

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

[0063] Specifically, in step (3), the concentration of the SDS-coated SiO 2 nanoparticles in the poor solvent is 10 to 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 to 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 concentration range above, a better structure of SiO 2 monolayer coating on NaCl can be formed. When the relative concentration of NaCl is relatively high, incomplete coating will occur, resulting in a decrease in hygroscopicity and warm cloud catalytic ability. When the relative concentration of NaCl is relatively high, an over-coated structure will be formed, and the outer layer of SiO 2 is prone to falling off or forming clusters, resulting in a decrease in the warm cloud catalytic performance of the material.

[0065] Specifically, in step (4), the poor solvent - SiO 2The total flow rate of the phase and the NaCl solution is 1-10 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 set within this range, the prepared NaCl-SiO 2 The crystal particle size is within the range of 1-10 microns required for warm cloud catalysts. When the flow rate is too low, the NaCl-SiO 2 The crystal particle size is too large, while when the flow rate is too high, the NaCl-SiO 2 The crystal particle size is too small, and the particle size distribution is too wide, reducing the warm cloud catalytic performance of the material.

[0067] Specifically, in step (4), the filtrate is obtained by filtration. After subjecting the filtrate to vacuum distillation, a poor solvent and water are obtained, which can be recycled by returning to step (3).

[0068] It should be noted that in step (4), the poor solvent-SiO 2 The phase and the NaCl solution are within the flow rate ratio range of the present invention. Because when it is lower than this range, the proportion of NaCl in the obtained product is too high, making it difficult to achieve the complete coating of SiO 2 on NaCl, resulting in a decrease in the hygroscopicity and cloud catalytic activity of the material; when it is higher than this range, SiO 2 is prone to self-aggregation phenomenon, that is, some SiO 2 nanoparticles are not coated on NaCl, but form SiO 2 clusters, resulting in a decrease in the overall hygroscopic performance of the product and a waste of materials.

[0069] The anti-solvent precipitation method is carried out based on the principle that NaCl first dissolves in a good solvent and then immediately forms NaCl crystal precipitation when entering a large amount of poor solvent. However, the usual anti-solvent precipitation method often has disadvantages such as excessive consumption of solvents, low crystal yield, and high time cost. The present invention uses a method of generating crystal precipitation with a continuous flow device to prepare micron-sized NaCl-SiO 2 crystals, and the poor solvent can be recycled, saving costs.

[0070] The NaCl-SiO 2 core-shell material obtained by the method of the present invention has the advantages of simple and convenient preparation process, low cost, and small environmental harm, and is confirmed to have excellent warm cloud artificial rainfall catalyst activity through hygroscopicity experiments, cloud chamber experiments, dynamic water vapor adsorption experiments, etc.

[0071] Another specific embodiment of the present invention discloses a warm cloud catalyst prepared by the above method. The warm cloud catalyst is SiO with hydroxyl groups coated on the surface of NaCl. 2 nanoparticles.

[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 the prior art, the warm cloud catalyst prepared by the method of the present invention is a single - layer coating of SiO formed with a NaCl core. 2 structure, and the prepared SiO 2 nanomaterials have hydroxyl groups (-OH) on the surface, which can form hydrogen bonds with water, thus making it easier to adsorb water vapor, forming local high humidity on the surface of NaCl, and promoting the hygroscopic growth of NaCl. Moreover, the particle size of NaCl meets the range of 1 - 10 μm required for the materials of warm cloud weather modification catalysts, which is the basis for being a good warm cloud weather modification catalyst.

[0074] The SiO 2 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 thickness of the coating layer is 40 - 370 nm, 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 following further explains and illustrates the technical solution of the present invention in combination with specific embodiments.

[0076] Example 1

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

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

[0079] (2) Add 6 mL of ultrapure water to the transparent solution, stir for 20 min, add 8 mL of TEOS, then add ammonia water to adjust the pH value to 6.5 - 7.5, and react at 40 °C for 12 h to obtain SiO 2 nanomaterials. Add 5 g of the SiO 2 nanomaterials and 0.1 g of sodium dodecyl sulfate (SDS) to 10 mL of ultrapure water, ultrasonicate for 2 h and then filter by suction. First, wash with ethanol 3 times, then wash with ultrapure water 3 times, and dry at a temperature of 60 °C and a pressure of 0.08 MPa for 12 hours to obtain SDS - coated SiO 2 nanoparticles;

[0080] (3) Add the SDS-coated SiO 2 nanoparticles to ethanol to obtain an ethanol-SiO 2 phase. The concentration of the SDS-coated SiO 2 nanoparticles in ethanol is 55 mg / mL. Dissolve NaCl in water to obtain an NaCl solution with a concentration of 1.75 mol / L;

[0081] (4) Mix the ethanol-SiO 2 phase and the NaCl solution at a flow rate ratio of 5:1. The total flow rate of the ethanol-SiO 2 phase and the NaCl solution is 2 mL / min. Mix, precipitate, and filter to obtain the warm cloud catalyst (i.e., NaCl-SiO 2 microparticles).

[0082] Example 2

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

[0084] (1) Add 0.1 g of cetyltrimethylammonium bromide to 50 mL of cyclohexane and stir for 10 min 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 TMOS, and then add ammonia water to adjust the pH value to 6.5 - 7.5. React at 35°C for 24 h to obtain SiO 2 nanomaterials. Add 5 g of the SiO 2 nanomaterials and 0.1 g of sodium dodecyl sulfate (SDS) to 10 mL of ultrapure water. After ultrasonic treatment for 1 h, perform suction filtration. First, wash with ethanol 4 times, then wash with ultrapure water 4 times, and dry at a temperature of 50°C and a pressure of 0.05 MPa for 10 hours to obtain SDS-coated SiO 2 nanoparticles,

[0086] (3) Add the SDS-coated SiO 2 nanoparticles to isopropanol to obtain an isopropanol-SiO 2 phase. The concentration of the SDS-coated SiO 2 nanoparticles in isopropanol is 10 mg / mL. Dissolve NaCl in water to obtain an NaCl solution with a concentration of 0.5 mol / L;

[0087] (4) Mix the isopropanol-SiO 2 phase and the NaCl solution at a flow rate ratio of 7:3. The isopropanol-SiO2 The total flow rate of the benzene and NaCl solution is 6 mL / min. Mix, precipitate, and filter to obtain the warm cloud catalyst (i.e., NaCl-SiO 2 micron particles).

[0088] Example 3

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

[0090] (1) Add 0.1 g of sodium dodecylbenzenesulfonate to 100 mL of n-hexane, stir for 30 min, then add 20 mL of n-butanol, and stir for 30 min until the solution is clear and transparent to 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, then add ammonia water to adjust the pH value to 6.5 - 7.5, and react at 45 °C for 4 h to obtain SiO 2 nanomaterials. Add 5 g of the SiO 2 nanomaterials and 0.1 g of sodium dodecyl sulfate (SDS) to 10 mL of ultrapure water, ultrasonicate for 1.5 h and then perform suction filtration. First, wash with ethanol 3 times, then wash with ultrapure water 3 times, and dry at a temperature of 70 °C and a pressure of 0.075 MPa for 11 hours to obtain SDS-coated SiO 2 nano-particles,

[0092] (3) Add the SDS-coated SiO 2 nano-particles to cyclohexane to obtain the cyclohexane-SiO 2 phase. The concentration of the SDS-coated SiO 2 nano-particles in cyclohexane is 100 mg / mL. Dissolve NaCl in water to obtain a NaCl solution with a concentration of 1.75 mol / L;

[0093] (4) Mix the cyclohexane-SiO 2 phase and the NaCl solution at a flow rate ratio of 9:1. The total flow rate of the cyclohexane-SiO 2 phase and the NaCl solution is 10 mL / min. Mix, precipitate, and filter to obtain the warm cloud catalyst (i.e., NaCl-SiO 2 micron particles).

[0094] Comparative Example 1

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

[0096] Comparative Example 2

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

[0098] Comparative Example 3

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

[0100] Comparative Example 4

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

[0102] Comparative Example 5

[0103] The preparation method of a warm cloud catalyst in this comparative example is the same as that in Example 1, except that in step (4), the ethanol-SiO 2 phase and the NaCl solution are mixed at a flow rate ratio of 10:1.

[0104] Comparative Example 6

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

[0106] Test Example 1

[0107] (a) Prepare warm cloud catalysts according to the methods of Examples 1-3 and Comparative Examples 1-6 respectively, and test the particle size of the SiO 2 nanomaterials obtained in step (2), and the central particle size of the warm cloud catalysts obtained in step (4), and the thickness of the SiO 2 nano-particles with hydroxyl groups coated, that is, the coating thickness. The results are shown in Table 1.

[0108] Among them, the central particle size test is the particle size distribution measured by an aerodynamic particle sizer (APS) when the catalyst material is dispersed in an 800 L smog chamber, and the coating layer thickness is tested by transmission electron microscopy (TEM).

[0109] Table 1

[0110]

[0111]

[0112] (2) Hygroscopicity performance test

[0113] The hygroscopicity of the material of the present invention was tested using a dynamic vapor sorption instrument.

[0114] The catalysts prepared in Examples 1-3 and Comparative Examples 1-6 were respectively subjected to hygroscopicity performance tests, and the results are shown in Table 2.

[0115] Table 2

[0116] Group Relative humidity at the start of moisture absorption / % 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 SiO 2 nanoparticles were not coated with SDS, its coating ability for NaCl decreased. Although the particle size of the SiO 2 nanoparticles was unchanged compared with that in Example 1, the central particle size and the coating layer thickness of the warm cloud catalyst decreased, indicating that the synthesized warm cloud catalyst material was not successfully coated;

[0118] In Comparative Example 2, since the temperature was too low during the synthesis of the SiO 2 nanoparticles, the particle size of the synthesized SiO 2 nanoparticles was too low. Although a single-layer coating could be formed, the small SiO 2 nanoparticles had poor hygroscopic ability, and the performance of the prepared warm cloud catalyst was poor;

[0119] In Comparative Example 3, since the temperature was too high during the synthesis of the SiO 2 nanoparticles, the particle size of the synthesized SiO 2 nanoparticles was too high. The large SiO 2 nanoparticles had poor coating performance and it was difficult to form a single-layer coating structure, resulting in a decrease in the performance of the warm cloud catalyst;

[0120] In Comparative Example 4, the flow rate ratio of the ethanol-SiO 2 phase was too low, that is, the proportion of SiO 2 nanoparticles in the obtained product was relatively low, resulting in incomplete coating, a smaller measured coating layer thickness, and thus a poor effect of the prepared warm cloud catalyst;

[0121] In Comparative Example 5, the flow rate ratio of the ethanol-SiO 2 phase was too high, that is, the proportion of SiO 2 nanoparticles in the obtained product was relatively high, resulting in an overly thick coating layer, not a single-layer coating, and a too large central particle size, making the hygroscopic performance of the material poor;

[0122] In Comparative Example 6, the addition amount of n-hexane was too low, resulting in the synthesized SiO 2The particle size of the nanoparticles is too small and the coating ability is poor, resulting in a low thickness of the coating layer, and the hygroscopic effect of the prepared warm cloud catalyst is poor.

[0123] Test Example 2

[0124] The warm cloud catalyst prepared in Example 1 was used in the Beijing Aerosol and Cloud Interaction Chamber (BACIC) of the Beijing Artificial Weather Modification Science Experiment Base to conduct the catalytic precipitation process under simulated warm cloud conditions. The BACIC is 70m 3 The schematic diagram of the cloud chamber is as Figure 1 shown.

[0125] The volume of the Beijing Aerosol and Cloud Interaction Chamber is 70m 3 , which can be approximately regarded as a cylinder with a diameter of 2.6m and a height of 14m. The controllable temperature range is -45°C to room temperature, and the controllable pressure is 1hPa to atmospheric pressure. The actual cloud environment is simulated by the method of expanding into clouds. The cloud chamber is equipped with a 3772-type particle counter (CPC), a 3938-type scanning mobility particle sizer (SMPS), and a 3321-type aerodynamic particle sizer (APS) produced by TSI Company of the United States to measure the aerosol number concentration spectrum with a particle size range of 0.5 - 20μm, which are used to measure the aerosol number concentration above 3nm, the aerosol number concentration spectrum in the particle size range of 0.02 - 0.7μm, and the aerosol number concentration spectrum in the particle size range of 0.5 - 20μm respectively, so as to realize the measurement of the aerosol number spectrum with a relatively wide coverage range from small particle size to large particle size before expanding into clouds. After adiabatic expansion into clouds, the pressure in the cloud chamber decreases, and the particle sizer cannot work properly when the pressure is lower than the standard atmospheric pressure. Therefore, for the warm cloud artificial weather catalyst after cloud formation to undergo the hygroscopic growth process as condensation nuclei, an FM-120 droplet spectrometer is required to measure the raindrop particle size in the range of 2 - 50μm generated.

[0126] As Figure 2 , through the comparison of the aerodynamic median diameter (MVD) in the cloud chamber experimental droplet spectrum, it can be intuitively seen that the median diameter of the water droplets generated by the NaCl-SiO 2 warm cloud catalyst prepared in Example 1 is about 45μm, while the median diameter of the water droplets formed by pure NaCl is only about 30μm, that is, the NaCl-SiO 2 material has stronger performance in catalytic warm cloud artificial rainfall.

[0127] As Figure 4 , from the cloud chamber CPC data, when 0.5g of NaCl and 0.5g of the NaCl-SiO 2 material prepared in Example 1 are input in the same way, the NaCl-SiO 2The number concentration of the warm cloud weather modification catalyst before the humidity reaches supersaturation is about 230 per cm 3 , while the number concentration of pure NaCl is only 70 per cm 3 . This indicates that the NaCl-SiO 2 weather modification catalyst material has better dispersibility, which is related to the fact that after surface coating with SiO 2 , the NaCl micron particles are separated, reducing the electrostatic effect between the NaCl micron particles.

[0128] The water vapor adsorption volumes of pure NaCl and NaCl-SiO 2 prepared in Examples 1-3 at different relative humidities are as Figure 3 shown. The NaCl-SiO 2 material achieves strong water vapor adsorption ability at low relative humidity. At the same time, compared with pure NaCl which starts to deliquesce at 75% RH, the NaCl-SiO 2 material deliquesces in advance at 68% - 71% RH. The earlier deliquescence enables the corresponding warm cloud catalyst material to initiate the collision and growth process earlier, improving the catalytic efficiency and being applicable to more cloud types.

[0129] The inventors also conducted the above experiments on the catalysts prepared in other examples, and the results were basically the same. Due to limited space, they are not listed one by one here.

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

Claims

1. A method for preparing a warm cloud catalyst, characterized in that: The steps include: (1) adding a surfactant to an organic solvent, then adding a co-surfactant, and stirring to obtain a transparent solution; (2) adding water, a silicon source, and a catalyst to the transparent solution to react to obtain SiO2 nanomaterials, adding sodium dodecyl sulfate to the SiO2 nanomaterials, ultrasonicating, washing, and drying to obtain SDS-coated SiO2 nanoparticles; (3) adding the SDS-coated SiO2 nanoparticles into a poor solvent to obtain a poor solvent-SiO2 phase; dissolving NaCl in water to obtain a NaCl solution; (4) The poor solvent-SiO2 phase and the NaCl solution are mixed at a flow rate ratio of 7:3-9:1, precipitated, and filtered to obtain the warm cloud catalyst.

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; The surfactant includes one or more of a nonionic surfactant, a cationic surfactant or an anionic surfactant; The co-surfactant includes alcohol.

3. The method for preparing a warm cloud catalyst according to claim 2, characterized in that: The nonionic surfactant includes one or more of Triton X-100, alkyl polyoxyethylene ether, and glyceride; The cationic surfactant includes one or more of cetyltrimethylammonium bromide, cationic panthenol, and cationic silicone oil; The anionic surfactant includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium fatty alcohol ether sulfate.

4. A method for preparing a warm cloud catalyst according to any one of claims 1 to 3, characterized in that: In step (1), the volume ratio of the organic solvent, the surfactant and the co-surfactant is 50-100:10-30:5-20.

5. A method for preparing a warm cloud catalyst according to any one of claims 1 to 3, characterized in that: 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.

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

7. 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 30-500nm.

8. 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 poor solvent is 10-100 mg / mL, and the concentration of the NaCl solution is 0.5-3 mol / L.

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

10. A warm cloud catalyst prepared by the method of any one of claims 1 to 9, characterized in that: 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.

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