Hydrophobic silicon dioxide aerogel based on desert sand as well as preparation method and application of hydrophobic silicon dioxide aerogel

Abstract

The invention relates to the technical field of preparation of silicon dioxide aerogel, in particular to hydrophobic silicon dioxide aerogel based on desert sand as well as a preparation method and application of the hydrophobic silicon dioxide aerogel. The preparation method comprises the following steps: S1, pretreatment; s2, calcining and activating; s3, preparing a water glass solution; s4, preparing wet gel; s5, replacement modification; s6, drying at normal pressure to obtain the hydrophobic silicon dioxide aerogel based on the desert sand. The invention provides hydrophobic silicon dioxide aerogel based on desert sand as well as a preparation method and application of the hydrophobic silicon dioxide aerogel, and aims to solve the problems of insufficient mechanical strength and relatively low porosity of a product prepared from silicon dioxide aerogel taking desert sand as a raw material in related technologies.

Description

Technical Field

[0001] This application relates to the technical field of silica aerogel preparation, and particularly relates to a hydrophobic silica aerogel based on desert sand, its preparation method and application. Background Art

[0002] Aerogel is an open-cell nanoporous material, usually made from a gel in which the liquid component of the gel is replaced by a gas. Its unique physical properties include low density, low thermal conductivity, large specific surface area, low refractive index and low dielectric constant. Due to these special properties, aerogels have great application potential in many fields and have attracted wide attention.

[0003] Silica aerogel is produced by removing the solvent from the wet gel while maintaining the integrity and high porosity of the gel. Supercritical fluid drying and atmospheric pressure drying are the most commonly used drying methods. Generally, the surface tension of a fluid under supercritical pressure is almost zero. This avoids collapse and shrinkage caused by surface tension, thus eliminating the fluid. However, supercritical drying involves high pressure, requires greater power and high-quality manufacturing equipment, and the supercritical drying process is cumbersome and time-consuming, which limits its commercial application. Therefore, in recent years, synthesizing silica aerogel using atmospheric pressure drying technology has attracted much attention. In order to further reduce the manufacturing cost and achieve the commercial production of silica aerogel, it is very necessary to use a cheaper silicon source as a precursor to synthesize a new process for hydrophobic silica aerogel in a reasonable way and at a reasonable cost.

[0004] Land desertification is one of the most serious ecological and environmental problems faced by the world today. It not only hinders the sustainable development of modern society, but also causes the continuous deterioration of the ecological environment, thus affecting the environment for human survival and development. There is a considerable amount of desert in the northwest region of China. The sand reserves in the desert are huge and rich in resources. At the same time, the desert sand contains abundant silica. If desert sand is used as a precursor for preparing aerogel, it can not only reduce the preparation cost, but also be of great significance for the green and sustainable development of the ecological environment.

[0005] However, due to the low specific surface area and mechanical strength of sand itself, the silica aerogel obtained by manufacturing usually has insufficient mechanical strength and low porosity, and its application range is limited. Summary of the Invention

[0006] This application provides a hydrophobic silica aerogel based on desert sand, its preparation method and application, so as to solve the problems in the related technology that the products prepared from silica aerogel using desert sand as a raw material have insufficient mechanical strength and low porosity.

[0007] In a first aspect, a method for preparing a hydrophobic silica aerogel based on desert sand is provided, which comprises the following steps: S1. Pretreatment: After washing the desert sand with water, it is immersed in a 5% hydrochloric acid solution for 2 - 3 h, filtered, and rinsed with deionized water until the rinsed water is neutral; It is ball - milled through a 200 - mesh sieve, and magnetic substances are removed by magnetic separation to obtain a powder. After mixing the powder with a dispersion solution, it is filtered to obtain a pretreated powder. The mass - to - volume ratio of the powder to the dispersion solution is 1 g:(5 - 10) mL; S2. Calcination activation: After uniformly mixing the pretreated powder and sesquicarbonate in a mass ratio of 1:0.2, it is heated to 600 - 750 °C at a heating rate of 5 - 10 °C / min and held for 2 h to complete the calcination activation, obtaining an activated slag; S3. Preparation of water - glass solution: The activated slag and sodium hydroxide are mixed in a mass ratio of 1:(0.5 - 0.8), deionized water is added to make the solid - to - liquid ratio reach 1:3, and it is stirred at 80 °C for 3 - 5 h, then filtered to obtain a clear solution; A 0.5 wt% cetyltrimethylammonium bromide solution is added to the clear solution, and it is left to age for 1 h to obtain a water - glass solution. The mass ratio of the cetyltrimethylammonium bromide solution to the clear solution is 1:5; S4. Preparation of wet gel: Under stirring conditions, a 10 wt% hydrochloric acid solution is added dropwise to the water - glass solution until the pH is 8 - 9, then a 0.1 wt% sodium citrate solution is added dropwise, and it is stirred and reacted for 1 - 2 h. Then 5 wt% ammonia water is added dropwise to adjust the solution pH to 9 - 10, and it is left to age at room temperature for 12 - 24 h to obtain a wet gel with a three - dimensional network skeleton structure; The volume ratio of the sodium citrate solution to the water - glass solution is 1:10; S5. Replacement modification: The wet gel prepared in S4 is immersed in absolute ethanol for 3 - 4 h, taken out and then immersed in a dimethyl carbonate solution for 3 - 4 h; After continuing to soak in the modification solution for 3 - 4 h, it is taken out and washed with absolute ethanol; It is continuously soaked in an absolute ethanol solution of 2 - 5 wt% trimethoxymethylsilane and reacted at 50 - 60 °C for 3 h to complete the replacement modification; S6. Atmospheric drying to obtain a hydrophobic silica aerogel based on desert sand: Use filter paper to absorb the surface moisture of the wet gel modified by S5 replacement, place it in a drying oven, and slowly heat it to 60~120℃ at a heating rate of 1~2℃ / min. The drying time is 6h to obtain a hydrophobic silica aerogel based on desert sand.

[0008] Preferably, in S1, the dispersion solution comprises 0.5 wt% lanolin ethanol solution and 0.5 wt% sodium chloroethyl sulfonate solution in a volume ratio of 1:1.

[0009] Preferably, in S4, while adding the sodium citrate solution, a modified suspension is also added, and the volume ratio of the modified suspension to the water glass solution is 1:(10-20).

[0010] Preferably, the method for preparing the modified suspension comprises the following steps: Dissolving the fullerene derivative C60 in anhydrous ethanol at a mass ratio of 0.1:100, and then adding cerium oxide nanoparticles to obtain a dispersion, wherein the mass ratio of the cerium oxide nanoparticles to the fullerene derivative C60 is 1:1; Dopamine hydrochloride was dissolved in ammonia water to obtain a 0.1 wt % dopamine hydrochloride solution, which was added to the dispersion to obtain a modified suspension. The mass ratio of the dopamine hydrochloride solution to the dispersion was 1:5.

[0011] Preferably, the particle size of the cerium oxide nanoparticles is 5 to 20 nm.

[0012] Preferably, the modified solution is a mixed solution of lithium stearate and sodium dodecylbenzene sulfonate, the concentration of lithium stearate is 1wt%, and the mass ratio of lithium stearate to sodium dodecylbenzene sulfonate is 1:1.

[0013] Preferably, in S1, when the powder and the dispersed solution are mixed, ultrasonic treatment is adopted, and the ultrasonic frequency is 40-60kHz, the power is 200-300W, and the time is 20-30min.

[0014] Preferably, in S6, the drying oven includes a normal pressure drying oven and a blast drying oven; After using filter paper to absorb the surface moisture of the wet gel after S5 replacement modification, the following steps are also included: First, dry in a normal pressure drying oven under ventilation at room temperature for 12 hours, and then dry at 60-120℃; When drying at 60-120°C, the method further comprises the following steps: The drying was carried out step by step in a forced air drying oven at temperatures of 60°C, 90°C and 120°C, respectively, and the drying time at each temperature was 2h.

[0015] In a second aspect, a hydrophobic silica aerogel based on desert sand is provided, which is prepared by the preparation method of the hydrophobic silica aerogel based on desert sand described in any one of the above.

[0016] In a third aspect, an application of the hydrophobic silica aerogel based on desert sand described above in a composite thermal insulation material is provided.

[0017] The beneficial effects brought by the technical solutions provided in this application include: This application provides a hydrophobic silica aerogel based on desert sand, its preparation method and application. Abundant and inexpensive desert sand is used as the raw material. In the pretreatment step, hydrochloric acid reacts with impurities such as calcium carbonate that may exist to remove impurities, and then the desert sand particles are dispersed by a dispersion liquid to ensure the dispersion of the desert sand particles during calcination activation. During calcination, sesquicarbonate decomposes to produce carbon dioxide and sodium carbonate. The carbon dioxide gas forms tiny pores in the material and provides an alkaline environment to promote the dissolution of silica in the desert sand. When preparing the wet gel, sodium citrate and a modification suspension are added. Through the complexation of sodium citrate with metal ions in the solution, the hydrolysis rate of sodium silicate is delayed, avoiding uneven gel caused by too fast local hydrolysis, thereby controlling the sol-gel reaction rate. The modification suspension enhances the mechanical strength of the aerogel. Then, through replacement modification, the aerogel forms a uniform pore structure, improving the surface hydrophobicity and water resistance of the aerogel; finally, atmospheric drying further reduces costs, reduces the problem of desert sand accumulation and production costs. At the same time, the obtained aerogel material has good mechanical strength, broadening the application field of desert sand. Therefore, it can solve the related problems mentioned in the background technology to a certain extent. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 It is a flowchart of the preparation method of the hydrophobic silica aerogel based on desert sand provided by this application; Figure 2 It is a photo of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided by this application; Figure 3 It is a scanning electron microscope image of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided by this application; Figure 4Hydrophobic angle diagram of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided by this application; Figure 5 Fourier infrared spectrum diagram of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided by this application; Figure 6 Thermal conductivity diagram and compressive strength schematic diagram of composite thermal insulation materials with different dosages of hydrophobic silica aerogel based on desert sand provided by this application. Detailed implementation manners

[0020] To make the objectives, technical solutions and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0021] See Figures 1 to 6 As shown, this application provides a hydrophobic silica aerogel based on desert sand, its preparation method and application.

[0022] Example 1 The preparation method of the hydrophobic silica aerogel based on desert sand provided in this example includes the following steps: S101. Pretreatment: After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 2 h, filter and rinse with deionized water until the rinsed water is neutral; Ball mill and pass through a 200-mesh sieve, remove magnetic substances by magnetic separation to obtain powder. Take 500 g of the powder and ultrasonically mix it with 4 L of a dispersion solution, then filter to obtain pretreated powder, where the ultrasonic frequency is 50 kHz, the power is 200 W, and the time is 25 min; S102. Calcination activation: Take 500 g of pretreated powder and mix it evenly with 100 g of sesquisodium carbonate, heat it to 650 °C at a heating rate of 5 °C / min, and keep it warm for 2 h to complete calcination activation and obtain activated slag; S103. Prepare a water glass solution: Take 500 g of activated slag and mix it with 300 g of sodium hydroxide, add 2.4 L of deionized water to make the solid-liquid ratio reach 1:3, stir at 80 °C for 4 h, and then filter to obtain a clear solution; Add 640 mL of a 0.5 wt% cetyltrimethylammonium bromide solution to the clear solution, and let it stand for aging for 1 h to obtain a water glass solution; S104. Prepare a wet gel: Under stirring conditions, a 10 wt% hydrochloric acid solution was added dropwise to 2 L of the sodium silicate solution prepared in S103 until the pH reached 8, and then 200 mL of a 0.1 wt% sodium citrate solution and 125 mL of a modified suspension were added dropwise. The mixture was stirred and reacted for 2 h, and then 5 wt% ammonia water was added dropwise to adjust the pH of the solution to 9. It was left to age at room temperature for 24 h to obtain a wet gel with a three-dimensional spatial network skeleton structure; S105, replacement modification: The wet gel prepared in S104 was immersed in absolute ethanol for 3 h, and after taking it out, it was continuously immersed in a dimethyl carbonate solution for 3 h; After continuously soaking in the modification solution for 4 h, it was taken out and washed with absolute ethanol; It was continuously immersed in an absolute ethanol solution of 3 wt% trimethoxymethylsilane and reacted at 55 °C for 3 h to complete the replacement modification; S106, atmospheric drying, to obtain a hydrophobic silica aerogel based on desert sand: Using filter paper, after sucking off the surface moisture of the wet gel modified in S105, it was first dried in an atmospheric drying oven at room temperature with ventilation for 12 h, and then gradually dried in a forced-air drying oven. At a heating rate of 2 °C / min, it was heated to three temperatures in sequence, and the temperatures were 60 °C, 90 °C, and 120 °C in sequence. And it was paused for heating and drying at 60 °C, 90 °C, and 120 °C, and the drying time at each temperature was 2 h.

[0023] Among them, the S101 dispersion solution is: a mixture of 2 L of a 0.5 wt% lanolin ethanol solution and 2 L of a 0.5 wt% sodium 2-chloroethylsulfonate solution.

[0024] The preparation method of the modified suspension in S104 includes the following steps: 0.12 g of fullerene derivative C60 was dissolved in 120 g of absolute ethanol, and then 0.12 g of cerium oxide nanoparticles (particle size 8 - 10 nm) was added to obtain a dispersion; 0.05 g of dopamine hydrochloride was dissolved in 50 g of 25% ammonia water to obtain a 0.1 wt% dopamine hydrochloride solution, and 24 g of the dopamine hydrochloride solution was added to the above dispersion to obtain a modified suspension.

[0025] The modification solution in S105 is: a mixture of 2 L of a 1 wt% lithium stearate solution and 2 L of a 1 wt% sodium dodecylbenzenesulfonate.

[0026] Example 2 The difference from Example 1 is that S6 includes the following steps: The surface moisture of the wet gel after S5 replacement modification was absorbed by filter paper, and then placed in a drying oven and slowly heated to 100°C at a heating rate of 2°C / min for 6 hours to obtain a hydrophobic silica aerogel based on desert sand.

[0027] Example 3 The difference from Example 1 is that no modification suspension is added to S4.

[0028] Example 4 The method for preparing the hydrophobic silica aerogel based on desert sand provided in this embodiment comprises the following steps: S401, pre-processing: After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 3 h, filter it, and rinse it with deionized water until the rinsed water is neutral; The powder was obtained by ball milling through a 200-mesh sieve and magnetic separation to remove magnetic substances. 500 g of the powder was mixed with 2.5 L of the dispersion solution by ultrasonication and filtered to obtain the pretreated powder. The ultrasonic frequency was 60 kHz, the power was 200 W, and the time was 20 min. S402, Calcination Activation: 500 g of the pretreated powder was mixed evenly with 100 g of sodium sesquicarbonate, and then heated to 750 ° C at a heating rate of 8 ° C / min, and kept warm for 2 hours to complete the calcination activation to obtain activated slag; S403, preparing water glass solution: Take 500g of activated slag and mix it with 250g of sodium hydroxide, add 2.25L of deionized water to make the solid-liquid ratio reach 1:3, stir at 80℃ for 3h, and filter to obtain a clear solution; Add 600 mL of 0.5 wt% hexadecyltrimethylammonium bromide solution to the clear solution, and allow to stand for 1 hour to obtain a water glass solution; S404, preparing wet gel: Under stirring conditions, 10 wt % hydrochloric acid solution was added dropwise to 2 L of the water glass solution prepared by S403 until the pH value was 9, and then 200 mL of 0.1 wt % sodium citrate solution and 100 mL of the modified suspension were added dropwise, and the reaction was stirred for 1 h, and 5 wt % ammonia water was added dropwise to adjust the solution pH value to 10, and the solution was aged at room temperature for 20 h to obtain a wet gel having a three-dimensional network skeleton structure; S405, substitution modification: The wet gel prepared by S404 was immersed in anhydrous ethanol for 3 h, and then taken out and immersed in dimethyl carbonate solution for another 3 h; After continuing to immerse in the modified solution for 3 h, take it out and wash it with anhydrous ethanol; Continue to soak in an absolute ethanol solution of 5 wt% trimethoxymethylsilane and react at 50 °C for 3 h to complete the replacement modification; S406. Dry at atmospheric pressure to obtain hydrophobic silica aerogel based on desert sand: Using filter paper, after sucking the surface moisture of the wet gel after the replacement modification of S405, first dry it in a normal pressure drying oven at room temperature for 12 h with ventilation, and then perform step-by-step drying in a forced-air drying oven. With a heating rate of 2 °C / min, heat it to three temperatures in sequence, and the temperatures are 60 °C, 90 °C, and 120 °C in sequence. And pause heating for drying at the temperatures of 60 °C, 90 °C, and 120 °C, and the drying time at each temperature is 2 h.

[0029] Among them, the dispersion solution in S401, the modification suspension in S404, and the modification solution in S405 are the same as those in Example 1.

[0030] Example 5 The preparation method of the hydrophobic silica aerogel based on desert sand provided in this example includes the following steps: S501. Pretreatment: After washing the desert sand with water, soak it in a 5% hydrochloric acid solution for 2 h, filter and rinse it with deionized water until the rinsed water is neutral; Ball mill and sieve through a 200-mesh sieve, remove magnetic substances by magnetic separation to obtain powder. Take 500 g of powder and ultrasonically mix it with 5 L of dispersion solution, and then filter to obtain pretreated powder. Among them, the ultrasonic frequency is 40 kHz, the power is 300 W, and the time is 30 min; S502. Calcination activation: Take 500 g of pretreated powder and mix it evenly with 100 g of sesquisodium carbonate, heat it to 600 °C at a heating rate of 10 °C / min, and keep it warm for 2 h to complete the calcination activation to obtain activated slag; S503. Prepare water glass solution: Take 500 g of activated slag and mix it with 400 g of sodium hydroxide, add 2.7 L of deionized water to make the solid-liquid ratio reach 1:3, stir at 80 °C for 5 h, and then filter to obtain a clear solution; Add 600 mL of a 0.5 wt% cetyltrimethylammonium bromide solution to the clear solution, and let it stand for aging for 1 h to obtain a water glass solution; S504. Prepare wet gel: Under stirring conditions, a 10 wt% hydrochloric acid solution was added dropwise to 2 L of the sodium silicate solution prepared in S503 until the pH reached 8. Then, 200 mL of a 0.1 wt% sodium citrate solution and 200 mL of a modification suspension were added dropwise, and the mixture was stirred and reacted for 1 h. Then, 5 wt% ammonia water was added dropwise to adjust the pH of the solution to 9, and the mixture was allowed to stand and age at room temperature for 12 h to obtain a wet gel with a three-dimensional network skeleton structure. S505. Displacement modification: The wet gel prepared in S504 was immersed in absolute ethanol for 4 h, and after taking it out, it was continuously immersed in a dimethyl carbonate solution for 4 h. After continuously immersing in the modification solution for 3 h, it was taken out and washed with absolute ethanol. It was continuously immersed in an absolute ethanol solution of 2 wt% trimethoxymethylsilane and reacted at 60 °C for 3 h to complete the displacement modification. S506. Atmospheric drying to obtain hydrophobic silica aerogel based on desert sand: Using filter paper, after sucking the surface moisture of the wet gel after displacement modification in S505, it was first dried in an atmospheric drying oven at room temperature with ventilation for 12 h, and then gradually dried in a forced-air drying oven. With a heating rate of 2 °C / min, it was heated to three temperatures in sequence, and the temperatures were 60 °C, 90 °C, and 120 °C in sequence. And it was paused for heating and drying at the temperatures of 60 °C, 90 °C, and 120 °C, and the drying time at each temperature was 2 h.

[0031] Among them, the modification solution in S505 is the same as that in Example 1.

[0032] The dispersion solution in S501 is: a mixture of 2.5 L of a 0.5 wt% lanolin ethanol solution and 2.5 L of a 0.5 wt% sodium 2-chloroethylsulfonate solution.

[0033] The preparation method of the modification suspension in S504 includes the following steps: 0.2 g of fullerene derivative C60 was dissolved in 200 g of absolute ethanol, and then 0.2 g of cerium oxide nanoparticles (particle size 10 - 20 nm) was added to obtain a dispersion. 0.05 g of dopamine hydrochloride was dissolved in 50 g of 25% ammonia water to obtain a 0.1 wt% dopamine hydrochloride solution, and 40 g of the dopamine hydrochloride solution was added to the above dispersion and mixed evenly to obtain the modification suspension.

[0034] Comparative Example 1 The difference from Example 1 is that S101 is replaced by the following steps: The desert sand was washed with water, immersed in a 5% hydrochloric acid solution for 2 h, filtered, and rinsed with deionized water until the rinsed water was neutral. The ball-milled powder was passed through a 200-mesh sieve, and magnetic substances were removed by magnetic separation to obtain the pretreated powder.

[0035] Comparative Example 2 The difference from Example 1 is that S102 was replaced with the following steps: Take 500 g of the pretreated powder, heat it to 650 °C at a heating rate of 5 °C / min, and hold for 2 h to complete calcination activation, obtaining the activated slag.

[0036] Comparative Example 3 The difference from Example 1 is that S104 and S105 were replaced with the following steps: Under magnetic stirring, 1 mol / L sulfuric acid was added to 2 L of the prepared sodium silicate solution to adjust its pH to 8, and a wet gel precursor was obtained after gelation; after aging the wet gel precursor for 24 h, it was placed in a 45 °C water bath for water washing to remove the Na + , obtaining a wet gel; The wet gel was soaked in absolute ethanol for 3 h for replacement, and this replacement was repeated 3 times to obtain an alcohol gel; a modified mixture was prepared, and the alcohol gel was placed in the modified mixture for surface modification replacement to complete the replacement modification.

[0037] Among them, the modified mixture includes n-hexane, ethanol, and trimethylchlorosilane (TMCS). The amount of n-hexane used is 50 mL, the molar ratio of TMCS to ethanol is 1, and the amount of TMCS used is 75% of the volume of the alcohol gel.

[0038] The hydrophobic silica aerogels based on desert sand (hereinafter referred to as aerogels) prepared by the preparation methods of Examples 1-5 and Comparative Examples 1-3 were tested.

[0039] Flexural strength test: Referring to GB / T232-2024 "Test Method for Bending of Metallic Materials", the aerogel was cut into a cuboid specimen of 10 mm×10 mm×50 mm (the length direction is the stress direction), ensuring that the surface is flat and crack-free; using a universal material testing machine (Instron5967), a three-point bending fixture (loading indenter radius 2 mm) was fixed on the testing machine, the distance between the two support points of the three-point bending fixture was adjusted to 40 mm, the specimen was placed flat on the two support points, ensuring that the specimen axis is perpendicular to the support points, the loading indenter was aligned with the center of the specimen, a preload of 0.01 N was applied, and then a vertical downward load was applied at a rate of 0.1 mm / min until the specimen broke, and the maximum failure load P max and the displacement at fracture were recorded. The calculation method of flexural strength is as follows:

[0040] Among them, MOR is the flexural strength (MPa), L is the support point spacing (40 mm), b is the specimen width (10 mm), h is the specimen thickness (10 mm), and P max is the maximum failure load at specimen fracture.

[0041] Tap density test: Grind the aerogel into powder with a particle size of 500 μm; weigh the graduated cylinder and record it as m1, pour the aerogel powder into the graduated cylinder until it reaches half of its volume; fix the graduated cylinder on the tap density tester, vibrate it at a frequency of 3 mm amplitude and 250 times / min for 10 min, and after completion, record the volume V of the aerogel powder and the weight m2 of the graduated cylinder + aerogel powder. The calculation method of tap density is as follows:

[0042] Among them, ρ is the tap density (g / cm 3 ).

[0043] See Table 1 for specific test results.

[0044] Table 1

[0045] The aerogel prepared in Example 1 has high flexural strength and low tap density, indicating that the desert sand is evenly dispersed during pretreatment and calcination activation, making the gel network have well-developed pores. In the modified suspension added during the preparation of the wet gel, the fullerene derivative C60 and cerium oxide nanoparticles form a composite reinforcement network. At the same time, dopamine hydrochloride and the modified solution replacement cross-linking and curing enhance the toughness of the skeleton and form stable hydrophobic channels. In the final drying step, the stepwise temperature increase also avoids pore collapse.

[0046] Compared with Example 1, in Example 2, the atmospheric drying method is different, the porosity is not much different, and the tap density is slightly higher. To a certain extent, it shows that the long-term constant temperature drying causes slight shrinkage of the gel network, more pore closure, and a decrease in the uniformity of the skeleton, thus resulting in a slightly lower flexural strength.

[0047] Compared with Example 1, in Example 3, the modified suspension was not added in S4, lacking the enhancement of C60 and cerium oxide nanoparticles. The gel skeleton is only composed of silica, with a fragile and easily breakable structure. Therefore, the flexural strength is significantly reduced, the porosity is reduced, and the tap density is increased.

[0048] Compared with Example 1, in Example 4, in the pretreatment step, the ratio of desert sand to the dispersion liquid increases (more desert sand), which leads to powder agglomeration. Also, due to the increase in the calcination activation temperature, the formed silica aerogel particles are denser and packed more tightly, resulting in an increase in tap density and a decrease in porosity.

[0049] Compared with Example 1, in Example 5, the ratio of desert sand to dispersion is reduced (too much dispersion), the powder concentration is low, and the ratio of sodium hydroxide is too high when preparing the water glass solution, the gelation process is difficult to control, and there are many skeleton defects; at the same time, the ratio of the modified suspension to the water glass solution is reduced, the nanoparticles are less supported, and the pores are easy to shrink, resulting in a decrease in porosity and an increase in tap density.

[0050] The flexural strength of the aerogels obtained in Comparative Examples 1 to 3 is significantly lower than that in Example 1. The tap density of Comparative Examples 1 and 2 is significantly increased and the porosity is significantly reduced. Since Comparative Example 1 was not dispersed by a dispersing solution during pretreatment, the pretreated powder obtained was severely agglomerated, and the product obtained by calcination was blocky, with a relatively loose structure and large pores between particles. In Comparative Example 2, sodium hemicarbonate was not doubled during calcination activation, and the quartz sand in the desert sand was not fully activated, and the silicon dioxide was not fully dissolved, resulting in insufficient activation. Comparative Example 3 replaced the modification with MCS modification. Although the hydrophobic effect was good, the molar ratio of TMCS to ethanol of 1:1 resulted in uneven modified layers and insufficient skeleton crosslinking, which led to lower flexural strength.

[0051] Furthermore, the aerogel prepared in Example 1 was characterized and analyzed, and the results are shown in Figures 2 to 5 As shown, Figure 2 This is a photo of the aerogel prepared in Example 1. Figure 3 For its microscopic picture, Figure 4 The hydrophobic angle diagram is shown in Figure 2. Figure 5 Its Fourier infrared spectrum.

[0052] In the hydrophobic angle diagram, the left and right contact angles are 141.4° and 141.3° respectively, with a difference of only 0.1°, indicating that the hydrophobicity of the aerogel surface is uniform, with no obvious local hydrophilic area, and the contact angle of about 141° belongs to the high hydrophobicity category (usually >120° is strongly hydrophobic), indicating that the aerogel surface has excellent hydrophobic properties. Figure 5 It can be seen that the strong absorption peak of Si-O-Si indicates that the aerogel has a typical silica network skeleton and a high structural density.

[0053] Furthermore, the present application provides an application of the above-prepared hydrophobic silica aerogel based on desert sand in a composite thermal insulation material. The composite thermal insulation material comprises cement, water, a silane coupling agent and the hydrophobic silica aerogel based on desert sand; The water-cement ratio is 0.35 (mass of water / mass of cement = 0.35), the silane coupling agent is γ-aminopropyltriethoxysilane, and the mass of the hydrophobic silica aerogel based on desert sand is 0.5~3% of the mass of cement.

[0054] Cement and water form a hardened matrix to provide structural support; silane coupling agent improves interfacial bonding; hydrophobic silica aerogel based on desert sand fills pores, reducing the thermal conductivity and enhancing the water resistance.

[0055] See Figure 6 , which is a graph of the thermal conductivity and a schematic diagram of the compressive strength of composite thermal insulation materials with different dosages of hydrophobic silica aerogel based on desert sand. The hydrophobic silica aerogel based on desert sand used therein is prepared as described in Example 1 above. It can be seen that as the dosage of hydrophobic silica aerogel based on desert sand increases, the compressive strength of the composite thermal insulation material decreases, and the thermal conductivity is improved. This application maximizes the thermal insulation effect without significantly reducing the matrix strength. Finally, it is considered that when the addition ratio of hydrophobic silica aerogel based on desert sand is 0.5%, the effect is the best. At this time, the composite thermal insulation material is suitable for fields such as building walls and pipeline insulation, while utilizing the low thermal conductivity and hydrophobicity of the aerogel, ensuring the workability and structural strength through the cement matrix.

[0056] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A preparation method of hydrophobic silica aerogel based on desert sand, characterized in that, It includes the following steps: S1. Pretreatment: After washing desert sand with water, soak it in a 5% hydrochloric acid solution for 2 - 3 h, filter it, and rinse it with deionized water until the rinsed water is neutral; Mill it through a 200 - mesh sieve, remove magnetic substances by magnetic separation to obtain powder. After mixing the powder with a dispersion solution, filter it to obtain pretreated powder. The mass - to - volume ratio of the powder to the dispersion solution is 1 g:(5 - 10) mL; S2. Calcination activation: After uniformly mixing the pretreated powder and sesquicarbonate in a mass ratio of 1:0.2, heat it at a heating rate of 5 - 10 °C / min to 600 - 750 °C and hold for 2 h to complete calcination activation and obtain activated slag; S3. Preparation of sodium silicate solution: Mix the activated slag and sodium hydroxide in a mass ratio of 1:(0.5 - 0.8), add deionized water to make the solid - to - liquid ratio reach 1:3, stir at 80 °C for 3 - 5 h, and then filter to obtain a clear solution; Add a 0.5 wt% cetyltrimethylammonium bromide solution to the clear solution, let it stand and age for 1 h to obtain a sodium silicate solution. The mass ratio of the cetyltrimethylammonium bromide solution to the clear solution is 1:5; S4. Preparation of wet gel: Under stirring conditions, dropwise add a 10 wt% hydrochloric acid solution to the sodium silicate solution until the pH is 8 - 9, then dropwise add a 0.1 wt% sodium citrate solution, stir and react for 1 - 2 h, dropwise add 5 wt% ammonia water to adjust the solution pH to 9 - 10, and let it stand and age at room temperature for 12 - 24 h to obtain a wet gel with a three - dimensional spatial network skeleton structure; The volume ratio of the sodium citrate solution to the sodium silicate solution is 1:10; S5. Displacement modification: Soak the wet gel prepared in S4 in absolute ethanol for 3 - 4 h, take it out and continue to soak it in a dimethyl carbonate solution for 3 - 4 h; Continue to soak it in a modification solution for 3 - 4 h, take it out and wash it with absolute ethanol; Continue to soak it in an absolute ethanol solution of 2 - 5 wt% trimethoxymethylsilane and react at 50 - 60 °C for 3 h to complete displacement modification; S6. Atmospheric drying to obtain hydrophobic silica aerogel based on desert sand: Use filter paper to blot the surface moisture of the wet gel after displacement modification in S5, place it in an oven, slowly heat it at a heating rate of 1 - 2 °C / min to 60 - 120 °C, and the drying duration is 6 h to obtain hydrophobic silica aerogel based on desert sand.

2. The preparation method of the hydrophobic silica aerogel based on desert sand according to claim 1, characterized in that: In S1, the dispersion solution includes a 0.5 wt% lanolin ethanol solution and a 0.5 wt% sodium 2 - chloroethylsulfonate solution with a volume ratio of 1:

1.

3. The preparation method of the hydrophobic silica aerogel based on desert sand according to claim 1, characterized in that: In S4, when adding the sodium citrate solution, it also includes adding a modification suspension. The volume ratio of the modification suspension to the sodium silicate solution is 1:(10 - 20).

4. The preparation method of the hydrophobic silica aerogel based on desert sand according to claim 3, characterized in that: The preparation method of the modified suspension comprises the following steps: Dissolving the fullerene derivative C60 in anhydrous ethanol at a mass ratio of 0.1:100, and then adding cerium oxide nanoparticles to obtain a dispersion, wherein the mass ratio of the cerium oxide nanoparticles to the fullerene derivative C60 is 1:1; Dopamine hydrochloride was dissolved in ammonia water to obtain a 0.1 wt % dopamine hydrochloride solution, which was added to the dispersion to obtain a modified suspension. The mass ratio of the dopamine hydrochloride solution to the dispersion was 1:

5.

5. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 4, characterized in that: The particle size of the cerium oxide nanoparticles is 5-20 nm.

6. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, characterized in that: The modified solution is a mixed solution of lithium stearate and sodium dodecylbenzene sulfonate, the concentration of lithium stearate is 1wt%, and the mass ratio of lithium stearate to sodium dodecylbenzene sulfonate is 1:

1.

7. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, characterized in that: In S1, when the powder and the dispersed solution are mixed, ultrasonic treatment is adopted, and the ultrasonic frequency is 40-60kHz, the power is 200-300W, and the time is 20-30min.

8. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, characterized in that: In S6, the drying oven includes a normal pressure drying oven and a blast drying oven; After using filter paper to absorb the surface moisture of the wet gel after S5 replacement modification, the following steps are also included: First, dry in a normal pressure drying oven under ventilation at room temperature for 12 hours, and then dry at 60-120℃; When drying at 60-120°C, the method further comprises the following steps: The drying was carried out step by step in a forced air drying oven at temperatures of 60°C, 90°C and 120°C, respectively, and the drying time at each temperature was 2h.

9. A hydrophobic silica aerogel based on desert sand, prepared by the method for preparing a hydrophobic silica aerogel based on desert sand according to any one of claims 1 to 8.

10. Use of the desert sand-based hydrophobic silica aerogel as claimed in claim 9 in composite thermal insulation materials.

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