Ceramic-based nanosheet / nanowire composite aerogel and preparation method thereof

Abstract

The present application relates to a kind of ceramic-based nanosheet / nanowire composite aerogel and its preparation method.The composite aerogel has the honeycomb mesh array structure formed by nanowire interpenetration interlacing;The ceramic-based nanosheet is in situ induced formation at the surface limit of nanowire, and is perpendicular to nanowire and evenly distributed on the outer surface of nanowire;The ceramic-based nanosheet presents ultra-thin and highly wrinkled morphology;The surface limit of the nanowire is the annular region within 2-100nm radially outward from the metal ions contained on the surface of nanowire.The mesh of the ceramic-based nanosheet / nanowire composite aerogel of the present application is microporous / mesoporous dual pore structure, with large specific surface area, which can effectively prevent the flow of air molecules, so that the composite aerogel has lower thermal conductivity;The shape and size of the ceramic-based nanosheet / nanowire composite aerogel of the present application are easy to control, and it is an ideal advanced thermal protection material.

Description

Technical Field

[0001] This invention relates to a ceramic-based nanosheet / nanowire composite aerogel and its preparation method, specifically to a high-temperature thermal insulation ceramic-based nanosheet / nanowire composite aerogel and its in-situ growth preparation method, belonging to the field of thermal protection materials technology. Background Technology

[0002] Aerogels are a type of gel composed of a nanoporous solid network, with a gaseous dispersed phase inside. Due to their ultra-high porosity and extremely small pore size, these materials exhibit ultra-low density and low thermal conductivity. Ceramic aerogels, in particular, possess characteristics such as high melting point, high-temperature oxidation resistance, large specific surface area, good chemical stability, and low thermal conductivity, making them widely used in defense, aerospace, civil engineering, and personal protective equipment, representing a promising emerging material. Currently, ceramic-based nanosheet composites are primarily used in electrocatalysis, mainly by increasing electron transport rates to enhance catalytic activity. Their high specific surface area increases the number of reactive sites during catalytic reactions, thereby improving the material's catalytic performance. Currently disclosed patents concerning methods for preparing ceramic-based nanosheet composite materials include: "A method for synthesizing α-phase nickel hydroxide nanosheets grown in situ on a carbon cloth substrate in one step (CN201910419436.7)" and "A core-shell type nickel hydroxide nanosheet / manganese cobalt oxide composite electrode material and its preparation method (CN201811344861.6)". However, the above preparation methods all involve placing the prepared mixed solution and the substrate together in a hydrothermal reactor. However, it is difficult for the metal ions in the mixed solution to be uniformly dispersed in various parts of the substrate, so it is impossible to obtain ceramic-based nanosheets with uniform distribution and good morphology and structure.

[0003] In addition, the published patents "A method for preparing a film using electrodeposition of cobalt hydroxide nanosheets, CN201811532328.2" and "A method for preparing a flexible electrode material of nanoporous nickel / nickel oxide supported ultrathin cobalt hydroxide nanosheets, CN201910746630.6" all use electrochemical deposition to obtain ceramic-based nanosheet structures. Due to the complicated process route, long synthesis cycle, and many influencing factors such as electrolyte, voltage, electrode, and deposition time, it is difficult to achieve size control and controllable growth of ceramic-based nanosheets. Furthermore, the bonding force between the nanosheets and the substrate is weak, resulting in the inability of their related application performance to meet actual needs. Summary of the Invention

[0004] The technical problem to be solved by this invention is that the process of synthesizing ceramic-based nanosheets by electrochemical deposition is complicated and has a long preparation cycle, and it is difficult to precisely control the size and morphology of ceramic-based nanosheets, which leads to unstable high-temperature thermal insulation performance of the material.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A ceramic-based nanosheet / nanowire composite aerogel is disclosed. The composite aerogel possesses a honeycomb mesh array structure formed by interlaced nanowires. The ceramic-based nanosheets are in-situ induced at the surface confinement of the nanowires, and are perpendicular to the nanowires and uniformly distributed on their outer surface. The ceramic-based nanosheets exhibit an ultrathin and highly wrinkled morphology. The surface confinement of the nanowires refers to a ring-shaped region within 2-100 nm radially outward from the metal ions contained on the nanowire surface. The mesh in the honeycomb mesh array structure is a dual-pore structure of micropores and mesopores. The micropores and mesopores of this dual-pore structure have a large specific surface area, effectively preventing the flow of air molecules, resulting in an ultra-low thermal conductivity for the composite aerogel.

[0007] Preferably, the honeycomb mesh array structure formed by interlacing nanowires is firmly bonded by an inorganic crosslinking agent, wherein the inorganic crosslinking agent is any one or a mixture of at least two of metal complex crosslinking agents, silicate crosslinking agents and precipitated crosslinking agents.

[0008] Preferably, the ceramic-based nanosheets have a height of 5-100 nm and a thickness of 0.5-5 nm; the nanowires have a length of 10-60 μm and a diameter of 20-80 nm; and the nanowires have 2-50 vertically and uniformly distributed ceramic-based nanosheets within a 10 nm × 10 nm region on their outer surface.

[0009] Preferably, the proportion of micropores in the ceramic-based nanosheet / nanowire composite aerogel is w%, and the proportion of mesopores is (1-w)%, where w ranges from 20% to 40%.

[0010] Preferably, the specific surface area of ​​the ceramic-based nanosheet / nanowire composite aerogel is 400-1200 m². 2 / g, with a room temperature thermal conductivity of less than 0.015 W / (m·K).

[0011] This invention also provides a method for preparing the above-mentioned ceramic-based nanosheet / nanowire composite aerogel, comprising the following steps:

[0012] Step (1): Disperse the inorganic nanoparticles in the solvent, add a certain proportion of catalyst, and stir rapidly at room temperature for 6-10 hours at a speed of 3000-8000 rpm until a homogeneous, non-settling inorganic nanoparticle dispersion is formed.

[0013] Step (2): Add a metal source to the inorganic nanoparticle dispersion obtained in step (1), and stir under pressure in a desorption bath (a desorption bath refers to the mixture after adding a metal source to the inorganic nanoparticle dispersion) for 4-8 hours (i.e., desorption) to prepare a homogeneous inorganic precursor solution.

[0014] Step (3): The inorganic precursor solution obtained in step (2) is placed in a hydrothermal reactor to synthesize an inorganic nanowire wet gel, wherein the metal source is uniformly distributed inside and on the outer surface of the entire nanowire.

[0015] Step (4): Place the inorganic nanowire wet gel obtained in step (3) in a displacement bath, add a certain amount of inorganic crosslinking agent, and after completing 3-5 solvent displacement treatments, place the inorganic nanowire wet gel in liquid nitrogen for rapid freezing treatment, and then obtain inorganic nanowire aerogel through supercritical drying process.

[0016] Step (5): The inorganic nanowire aerogel obtained in step (4) is subjected to ammonia vapor fumigation treatment, and then placed in a vacuum oven at a temperature of 80-130℃ for 4-8 hours to react. The aerogel after fumigation treatment undergoes chemical co-precipitation reaction with metal source ions under thermal induction environment, and nanosheets are vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowire. Finally, after high-temperature heat treatment, a structurally stable ceramic-based nanosheet / nanowire composite aerogel is obtained.

[0017] Preferably, the inorganic nanoparticles in step (1) are any one of silicon dioxide (SiO2, with a particle size of 10-40 nm), titanium dioxide (TiO2, with a particle size of 20-50 nm), zirconium dioxide (ZrO2, with a particle size of 15-45 nm), and aluminum oxide (Al2O3, with a particle size of 10-30 nm); the solvent is any one or a mixture of at least two of water, ethanol, ethylene glycol, propylene glycol, isopropanol, tert-butanol, benzyl alcohol, and diacetone alcohol; the catalyst is any one of acetic acid, hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid; and the mass concentration of the resulting inorganic nanoparticle dispersion is 10-45%.

[0018] Preferably, the metal source in step (2) is any one of titanium, zirconium, and aluminum; the mass ratio of the metal source to the inorganic nanoparticles is in the range of 1:5 to 1:20; the molar concentration of the inorganic acid in the desorption bath is 0.1-5 mol / L; the desorption bath is pressurized and stirred, wherein the conditions for the pressurized desorption test are: desorption pressure 1-4 MPa, desorption temperature 80-150℃.

[0019] Preferably, the hydrothermal reaction conditions in step (3) are: reaction temperature 150-300℃, reaction time 6-24h, and reaction pressure 2-10MPa.

[0020] Preferably, the displacement bath in step (4) is a low surface tension solvent, wherein the low surface tension solvent is one or a combination of at least two of benzene, toluene, n-hexane, cyclohexane, diethyl ether, acetone, dichloromethane or ethyl acetate, and its surface tension is less than 30 mN / m; wherein the mass concentration of the inorganic crosslinking agent is 0.5-5%.

[0021] Preferably, the ammonia vapor fumigation conditions in step (5) are: ammonia vapor flow rate 20-80 m / s, fumigation temperature 20-40℃, and fumigation time 1-5 h; the high-temperature heat treatment is high-temperature muffle furnace heat treatment, with the following conditions: heating rate 2-10℃ / min, calcination temperature 600-1400℃, calcination time 8-20 h, and holding time 1-4 h; the ceramic-based nanosheet / nanowire composite aerogel is one or a combination of at least two of SiO2-based, TiO2-based, ZrO2-based, and Al2O3-based.

[0022] This invention prepares a ceramic-based nanosheet / nanowire composite aerogel for high-temperature thermal insulation through the above steps, and its specific mechanism is as follows:

[0023] The ceramic-based nanosheets are formed through in-situ growth at confined locations on the nanowire surface via a chemical co-precipitation reaction. A metal source is uniformly distributed throughout the interior and outer surface of the nanowire. When the inorganic nanowire aerogel is fumigated in an ammonia vapor environment, extremely low concentrations of metal ions diffuse into the pores of the nanowire aerogel. When the metal ion concentration in the reaction system reaches supersaturation, hydroxide ions in the ammonia vapor are confined to the region near the metal source on the nanowire surface. This allows the metal ions to undergo heterogeneous nucleation reactions at the confined locations on the nanowire surface, resulting in an ultrathin and highly wrinkled ceramic-based nanosheet structure. Finally, high-temperature treatment yields a ceramic-based nanosheet / nanowire composite aerogel.

[0024] For the heterogeneous nucleation process of ceramic-based nanosheets, it is necessary to maintain the supersaturated metal ions at an extremely low concentration level. In the heterogeneous nucleation reaction initiated by the surface energy of the nanowires, the metal ions and ammonia vapor begin to slowly produce a chemical co-precipitation. Under thermal induction conditions, the nanosheets spontaneously and orderly grow vertically from the inside to the outside at the surface confinement of the nanowires. After high-temperature heat treatment, a structurally stable ceramic-based nanosheet / nanowire composite aerogel is obtained.

[0025] This aerogel has a regularly arranged honeycomb mesh array structure. Its basic formation mechanism can be attributed to the rapid freezing of the wet nanowire gel at an ultra-low temperature of -196℃ in liquid nitrogen. During the freezing process, solvent molecules grow vertically and form parallel cylindrical ice crystals. At this time, the nanowires are squeezed into the gaps between the columnar solvent ice crystals. The final supercritical drying process realizes the rapid sublimation of the ice crystals, while the nanowire network in the gaps between the ice crystals is retained, thus forming a nanowire aerogel with a regularly ordered honeycomb mesh array structure.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) An inorganic nanowire wet gel containing a metal source was prepared in one step by a hydrothermal synthesis reaction. Then, the nanowire wet gel was subjected to ammonia vapor fumigation and high-temperature thermal induction treatment, so that nanosheets were regularly and orderly grown in situ from radial to outward at the confined area of ​​the nanowire. Finally, after high-temperature heat treatment, a structurally stable ceramic-based nanosheet / nanowire composite aerogel was obtained. The nanosheets exhibited an ultrathin and highly wrinkled morphology with a height of 5-100 nm and a thickness of 0.5-5 nm.

[0028] (2) Nanowires play a key role in the entire reaction system. First, they promote the full and uniform distribution of metal sources throughout the nanowires. Second, they can act as a reaction carrier for in-situ co-precipitation between ammonia vapor and metal ions. In addition, they can effectively inhibit the aggregation of metal ions, which is beneficial to the controllable growth of ceramic-based nanosheets. Finally, they can serve as a substrate for in-situ growth of ceramic-based nanosheets, fixing the nanosheets on the outer surface of the nanowires, making the structure of ceramic-based nanosheet / nanowire composite aerogel more stable.

[0029] (3) Ceramic-based nanosheet / nanowire composite aerogels have a honeycomb mesh array structure formed by interlaced nanowires. The mesh has a dual pore structure of micropores and mesopores, with a large specific surface area, which can effectively prevent the flow of air molecules, resulting in low thermal conductivity of the composite aerogel. In addition, the shape and size of ceramic-based nanosheet / nanowire composite aerogels are easy to control, making them an ideal advanced thermal protection material. Attached Figure Description

[0030] Figure 1 Low-magnification scanning electron microscope image of ceramic-based nanosheet / nanowire composite aerogel;

[0031] Figure 2 High-magnification scanning electron microscope image of ceramic-based nanosheet / nanowire composite aerogel;

[0032] Figure 3 Transmission electron microscopy (TEM) images of ceramic-based nanosheets / nanowires. Detailed Implementation

[0033] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0034] Example 1

[0035] A method for preparing zirconium dioxide nanosheet / nanowire composite aerogel:

[0036] (1) Disperse 20g of zirconium dioxide nanoparticles (particle size: 20nm) into 110g of deionized water, then add 0.5g of hydrochloric acid solution (1mol / L), and stir rapidly at room temperature for 7h at a speed of 5000rpm until a homogeneous non-settling zirconium dioxide nanoparticle dispersion is formed.

[0037] (2) Add 4g of zirconium propoxide to the zirconium dioxide nanoparticle dispersion, and stir under pressure in a desorption bath for 4h, wherein the desorption pressure is 3MPa and the desorption temperature is 120℃, to prepare a homogeneous dispersed zirconium dioxide precursor solution.

[0038] (3) The zirconium dioxide precursor solution was placed in a 200mL hydrothermal reactor, the reaction temperature was 180℃, the reaction time was 10h, and the reaction pressure was 3MPa to synthesize zirconium dioxide nanowire wet gel, wherein zirconium ions were uniformly distributed in the interior and outer surface of the entire nanowire.

[0039] (4) The obtained zirconium nanowire wet gel was placed in a hexane replacement bath, and 0.5% methyltrimethoxysilane was added. After three solvent replacement treatments, the wet gel was placed in liquid nitrogen at -196℃ for rapid freezing treatment, and then zirconium nanowire aerogel was obtained by supercritical drying process.

[0040] (5) The above-mentioned zirconia nanowire aerogel was subjected to ammonia vapor fumigation treatment, wherein the ammonia vapor flow rate was 20 m / s, the fumigation temperature was 20℃, and the fumigation time was 3h; then it was placed in a vacuum oven at 80℃ for 4h to react, so that the aerogel after fumigation treatment could undergo chemical co-precipitation reaction with zirconium ions under thermal induction environment, and then zirconium hydroxide nanosheets were vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowires. Finally, after high-temperature muffle furnace heat treatment (heating rate 5℃ / min, calcination temperature 1000℃, calcination time 18h, and holding time 2h), a structurally stable zirconia nanosheet / nanowire composite aerogel was obtained.

[0041] The resulting zirconia nanosheet / nanowire composite aerogel possesses a honeycomb mesh array structure formed by interwoven zirconia nanowires. The zirconia nanosheets have an average height of 50 nm and an average thickness of 2 nm; the zirconia nanowires have an average length of 50 μm and an average diameter of 20 nm. An average of 5 zirconia nanosheets are vertically and uniformly distributed within a 10 nm × 10 nm region on the outer surface of each nanowire. The micropores account for 35% of the zirconia nanosheet / nanowire composite aerogel, the mesopores account for 65%, and the specific surface area is 650 m². 2 / g, with a thermal conductivity of 0.013 W / (m·K) at room temperature.

[0042] Figure 1 The image shows a SEM image (at a low magnification) of the zirconia nanosheet / nanowire composite aerogel, which illustrates the macroscopic structural morphology of the zirconia nanosheet / nanowire composite aerogel prepared in this patent, namely, a honeycomb mesh array structure with regular arrangement.

[0043] Figure 2 The image shows a high magnification SEM image of the zirconia nanosheet / nanowire composite aerogel. This image shows the microstructure and morphology of the zirconium hydroxide nanosheets in the zirconia nanosheet / nanowire composite aerogel prepared in this patent, that is, the zirconia nanosheets / nanowires in the aerogel are interwoven.

[0044] Figure 3 The image shows a transmission electron microscope (TEM) image of zirconium dioxide nanosheets / nanowires in an aerogel. This image further demonstrates that the zirconium dioxide nanosheets prepared in this patent exhibit an ultrathin and highly wrinkled morphology.

[0045] Example 2

[0046] A method for preparing zirconium dioxide nanosheet / nanowire composite aerogel:

[0047] (1) Disperse 25g of zirconium dioxide nanoparticles (particle size: 15nm) into 120g of deionized water, then add 0.8g of nitric acid (0.5mol / L) solution, and stir rapidly at room temperature for 8h at a speed of 4000rpm until a homogeneous non-settling zirconium dioxide nanoparticle dispersion is formed.

[0048] (2) Add 5g of zirconium isopropoxide to the zirconium dioxide nanoparticle dispersion, and stir under pressure in a desorption bath for 4h, wherein the desorption pressure is 2.5MPa and the desorption temperature is 110℃, to prepare a homogeneous dispersed zirconium dioxide precursor solution.

[0049] (3) The zirconium dioxide precursor solution was placed in a 200 mL hydrothermal reactor, the reaction temperature was 220 °C, the reaction time was 8 h, and the reaction pressure was 2.8 MPa to synthesize zirconium dioxide nanowire wet gel, wherein zirconium ions were uniformly distributed in the interior and outer surface of the entire nanowire.

[0050] (4) The obtained zirconium nanowire wet gel was placed in a hexane replacement bath, and 0.8% methyltriethoxysilane was added. After four solvent replacement treatments, the wet gel was placed in liquid nitrogen at -196℃ for rapid freezing treatment, and then zirconium nanowire aerogel was obtained by supercritical drying process.

[0051] (5) The above-mentioned zirconia nanowire aerogel was subjected to ammonia vapor fumigation treatment, wherein the ammonia vapor flow rate was 40 m / s, the fumigation temperature was 40℃, and the fumigation time was 2h; then it was placed in a vacuum oven at 90℃ for 5h to react, so that the aerogel after fumigation treatment could undergo chemical co-precipitation reaction with zirconium ions under thermal induction environment, and then zirconium hydroxide nanosheets were vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowires. Finally, after high-temperature muffle furnace heat treatment (heating rate 2℃ / min, calcination temperature 1100℃, calcination time 15h, and holding time 3h), a structurally stable zirconia nanosheet / nanowire composite aerogel was obtained.

[0052] The resulting zirconia nanosheet / nanowire composite aerogel possesses a honeycomb mesh array structure formed by interwoven zirconia nanowires. The zirconia nanosheets have an average height of 60 nm and an average thickness of 0.5 nm; the zirconia nanowires have an average length of 40 μm and an average diameter of 13 nm. An average of 20 zirconia nanosheets are vertically and uniformly distributed within a 10 nm × 10 nm region on the outer surface of the nanowires. The micropores account for 27% of the zirconia nanosheet / nanowire composite aerogel, the mesopores account for 73%, and the specific surface area is 720 m². 2 / g, with a thermal conductivity of 0.010 W / (m·K) at room temperature.

[0053] Example 3

[0054] A method for preparing titanium dioxide nanosheet / nanowire composite aerogel:

[0055] (1) Disperse 28g of titanium dioxide nanoparticles (particle size: 25nm) into 150g of deionized water, then add 0.2g of sulfuric acid solution (1mol / L), and stir rapidly at room temperature for 8h at a speed of 4000rpm until a homogeneous non-settling titanium dioxide nanoparticle dispersion is formed.

[0056] (2) Add 3.6g of tetraethanol titanium to the titanium dioxide nanoparticle dispersion, and stir under pressure in a desorption bath for 7.5h, wherein the desorption pressure is 2.6MPa and the desorption temperature is 130℃, to prepare a homogeneous dispersed titanium dioxide precursor solution.

[0057] (3) The titanium dioxide precursor solution was placed in a 200mL hydrothermal reactor, the reaction temperature was 230℃, the reaction time was 18h, and the reaction pressure was 3.1MPa to synthesize titanium dioxide nanowire wet gel, wherein titanium ions were uniformly distributed in the interior and outer surface of the entire nanowire.

[0058] (4) The obtained titanium dioxide nanowire wet gel was placed in a cyclohexane replacement bath, and 3.2% tetrabutoxysilane was added. After three solvent replacement treatments, the wet gel was placed in liquid nitrogen at -196℃ for rapid freezing treatment, and then titanium dioxide nanowire aerogel was obtained by supercritical drying process.

[0059] (5) The above titanium dioxide nanowire aerogel was subjected to ammonia vapor fumigation treatment, wherein the ammonia vapor flow rate was 80 m / s, the fumigation temperature was 22℃, and the fumigation time was 1.5 h; then it was placed in a vacuum oven at 100℃ for 5 h to react, so that the aerogel after fumigation treatment could undergo chemical co-precipitation reaction with titanium ions under thermal induction environment, and then titanium hydroxide nanosheets were vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowires. Finally, after high-temperature muffle furnace heat treatment (heating rate 3℃ / min, calcination temperature 700℃, calcination time 10 h, and holding time 2.5 h), a structurally stable titanium dioxide nanosheet / nanowire composite aerogel was obtained.

[0060] The obtained titanium dioxide nanosheet / nanowire composite aerogel has a honeycomb mesh array structure formed by interlaced titanium dioxide nanowires. The titanium dioxide nanosheets have an average height of 30 nm and an average thickness of 1.2 nm; the titanium dioxide nanowires have an average length of 15 μm and an average diameter of 28 nm. An average of 18 titanium dioxide nanosheets are vertically and uniformly distributed within a 10 nm × 10 nm region on the outer surface of the nanowires. The micropores account for 28% and the mesopores account for 72% of the total aerogel, with a specific surface area of ​​980 m². 2 / g, with a thermal conductivity of 0.011 W / (m·K) at room temperature.

[0061] Example 4

[0062] A method for preparing titanium dioxide nanosheet / nanowire composite aerogel:

[0063] (1) Disperse 23g of titanium dioxide nanoparticles (particle size: 25nm) into 167g of deionized water, then add 1.2g of phosphoric acid (1mol / L) solution, and stir rapidly at room temperature for 7h at a speed of 4800rpm until a homogeneous non-settling titanium dioxide nanoparticle dispersion is formed.

[0064] (2) Add 1.8 g of titanium butoxide to the titanium dioxide nanoparticle dispersion, and stir under pressure in a desorption bath for 5 h, wherein the desorption pressure is 3.5 MPa and the desorption temperature is 140 °C, to prepare a homogeneous dispersed titanium dioxide precursor solution.

[0065] (3) The titanium dioxide precursor solution was placed in a 250 mL hydrothermal reactor, the reaction temperature was 240 °C, the reaction time was 20 h, and the reaction pressure was 3.3 MPa to synthesize titanium dioxide nanowire wet gel, wherein titanium ions were uniformly distributed in the interior and outer surface of the entire nanowire.

[0066] (4) The obtained titanium dioxide nanowire wet gel was placed in a dichloromethane replacement bath, and 3.2% trimethylmethoxysilane was added. After five solvent replacement treatments, the wet gel was placed in liquid nitrogen at -196℃ for rapid freezing treatment, and then titanium dioxide nanowire aerogel was obtained by supercritical drying process.

[0067] (5) The above titanium dioxide nanowire aerogel was subjected to ammonia vapor fumigation treatment, wherein the ammonia vapor flow rate was 70 m / s, the fumigation temperature was 32℃, and the fumigation time was 3.5 h; then it was placed in a vacuum oven at 95℃ for 5.5 h to react, so that the aerogel after fumigation treatment could undergo a chemical co-precipitation reaction with titanium ions under thermal induction environment, and then titanium hydroxide nanosheets were vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowires. Finally, after high-temperature muffle furnace heat treatment (heating rate 4℃ / min, calcination temperature 700℃, calcination time 12 h, and holding time 3 h), a structurally stable titanium dioxide nanosheet / nanowire composite aerogel was obtained.

[0068] The obtained titanium dioxide nanosheet / nanowire composite aerogel has a honeycomb mesh array structure formed by interlaced titanium dioxide nanowires. The titanium dioxide nanosheets have an average height of 85 nm and an average thickness of 2.5 nm; the titanium dioxide nanowires have an average length of 35 μm and an average diameter of 38 nm. An average of four titanium dioxide nanosheets are vertically and uniformly distributed within a 10 nm × 10 nm region on the outer surface of the nanowires. The micropores account for 22% and the mesopores account for 78% of the total aerogel, with a specific surface area of ​​1120 m². 2 / g, with a thermal conductivity of 0.014 W / (m·K) at room temperature.

[0069] Example 5

[0070] A method for preparing alumina nanosheet / nanowire composite aerogel:

[0071] (1) Disperse 34g of alumina nanoparticles (particle size: 28nm) into 346g of deionized water, then add 1.8g of sulfuric acid (1.3mol / L) solution, and stir rapidly at room temperature for 9h at a speed of 7200rpm until a homogeneous alumina nanoparticle dispersion is formed.

[0072] (2) Add 2.4 g of aluminum sec-butoxide to the alumina nanoparticle dispersion, and stir under pressure in a desorption bath for 6 h, wherein the desorption pressure is 4 MPa and the desorption temperature is 150 °C, to prepare a homogeneous dispersed alumina precursor solution.

[0073] (3) The alumina precursor solution was placed in a 500mL hydrothermal reactor, the reaction temperature was 245℃, the reaction time was 13h, and the reaction pressure was 3.9MPa to synthesize alumina nanowire wet gel, wherein aluminum ions were uniformly distributed in the interior and outer surface of the entire nanowire.

[0074] (4) The obtained alumina nanowire wet gel was placed in an ethyl acetate replacement bath, and 1.2% tetraethyl orthosilicate was added. After three solvent replacement treatments, the wet gel was placed in liquid nitrogen at -196℃ for rapid freezing treatment, and then alumina nanowire aerogel was obtained by supercritical drying process.

[0075] (5) The above alumina nanowire aerogel was subjected to ammonia vapor fumigation treatment, wherein the ammonia vapor flow rate was 55 m / s, the fumigation temperature was 38℃, and the fumigation time was 4.5 h; then it was placed in a vacuum oven at 90℃ for 7 h to react, so that the aerogel after fumigation treatment could undergo chemical co-precipitation reaction with aluminum ions under thermal induction environment, and then aluminum hydroxide nanosheets were vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowires. Finally, after high-temperature muffle furnace heat treatment (heating rate 2℃ / min, calcination temperature 1200℃, calcination time 10 h, and holding time 2 h), a structurally stable alumina nanosheet / nanowire composite aerogel was obtained.

[0076] The resulting alumina nanosheet / nanowire composite aerogel possesses a honeycomb mesh array structure formed by interwoven alumina nanowires. The alumina nanosheets have an average height of 40 nm and an average thickness of 1.8 nm; the alumina nanowires have an average length of 42 μm and an average diameter of 34 nm. An average of 9 alumina nanosheets are vertically and uniformly distributed within a 10 nm × 10 nm region on the outer surface of the nanowires. The alumina nanosheet / nanowire composite aerogel exhibits a micropore content of 40%, a mesopore content of 60%, and a specific surface area of ​​1200 m². 2 / g, with a thermal conductivity of 0.015 W / (m·K) at room temperature.

[0077] Example 6

[0078] A method for preparing alumina nanosheet / nanowire composite aerogel:

[0079] (1) Disperse 37g of alumina nanoparticles (particle size: 30nm) into 263g of deionized water, then add 3.5g of acetic acid (5mol / L) solution, and stir rapidly at room temperature for 10h at a speed of 3000rpm until a homogeneous alumina nanoparticle dispersion is formed.

[0080] (2) Add 3.7g of aluminum tri-propoxy to the alumina nanoparticle dispersion, and stir under pressure in a desorption bath for 8h, wherein the desorption pressure is 1MPa and the desorption temperature is 80℃, to prepare a homogeneous dispersed alumina precursor solution.

[0081] (3) The alumina precursor solution was placed in a 500 mL hydrothermal reactor, the reaction temperature was 300 °C, the reaction time was 11 h, and the reaction pressure was 10 MPa to synthesize alumina nanowire wet gel, wherein aluminum ions were uniformly distributed in the interior and outer surface of the entire nanowire.

[0082] (4) The obtained alumina nanowire wet gel was placed in a toluene displacement bath, and tetraethyl orthosilicate with a mass concentration of 3% was added. After completing 5 solvent displacement treatments, the wet gel was placed in liquid nitrogen at -196℃ for rapid freezing treatment, and then alumina nanowire aerogel was obtained by supercritical drying process.

[0083] (5) The above alumina nanowire aerogel was subjected to ammonia vapor fumigation treatment, wherein the ammonia vapor flow rate was 20 m / s, the fumigation temperature was 20℃, and the fumigation time was 1 h; then it was placed in a vacuum oven at 130℃ for 8 h to react, so that the aerogel after fumigation treatment could undergo chemical co-precipitation reaction with aluminum ions under thermal induction environment, and then aluminum hydroxide nanosheets were vertically grown in situ from the inside to the outside at the confined area on the surface of the nanowires. Finally, after high-temperature muffle furnace heat treatment (heating rate 10℃ / min, calcination temperature 1400℃, calcination time 8.5 h, holding time 1 h), a structurally stable alumina nanosheet / nanowire composite aerogel was obtained.

[0084] The resulting alumina nanosheet / nanowire composite aerogel possesses a honeycomb mesh array structure formed by interwoven alumina nanowires. The alumina nanosheets have an average height of 100 nm and an average thickness of 5 nm; the alumina nanowires have an average length of 60 μm and an average diameter of 80 nm. On average, there are two vertically and uniformly distributed alumina nanosheets within a 10 nm × 10 nm region on the outer surface of each nanowire. The alumina nanosheet / nanowire composite aerogel exhibits a micropore content of 20%, a mesopore content of 80%, and a specific surface area of ​​890 m².2 / g, with a thermal conductivity of 0.009 W / (m·K) at room temperature.

[0085] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A ceramic-based nanosheet / nanowire composite aerogel, characterized in that, The composite aerogel has a honeycomb mesh array structure formed by interlacing nanowires; the ceramic-based nanosheets are in-situ induced at the surface confinement of the nanowires and are perpendicular to the nanowires and uniformly distributed on the outer surface of the nanowires. The ceramic-based nanosheets exhibit an ultrathin and wrinkled morphology; the surface confinement of the nanowires is a ring-shaped region within 2-100 nm radially outward of the metal ions contained on the nanowire surface; the mesh in the honeycomb array structure is a dual-pore structure of micropores and mesopores; the height of the ceramic-based nanosheets is 5-100 nm, and the thickness is 0.5-5 nm; the length of the nanowires is 10-60 μm, and the diameter is 20-80 nm; the number of vertically and uniformly distributed ceramic-based nanosheets in a 10 nm × 10 nm region on the outer surface of the nanowires is 2-50; the ceramic-based nanosheet / nanowire composite aerogel is one or a combination of at least two of SiO2-based, TiO2-based, ZrO2-based, and Al2O3-based materials.

2. The ceramic-based nanosheet / nanowire composite aerogel according to claim 1, characterized in that, The honeycomb mesh array structure formed by interlacing nanowires is firmly bonded by a crosslinking agent; the crosslinking agent is one of methyltrimethoxysilane, methyltriethoxysilane, tetra-n-butoxysilane, trimethylmethoxysilane, and tetraethyl orthosilicate.

3. The ceramic-based nanosheet / nanowire composite aerogel according to claim 1, characterized in that, The composite aerogel has a micropore ratio of w and a mesopore ratio of (1-w)%, where w ranges from 20% to 40%.

4. The ceramic-based nanosheet / nanowire composite aerogel according to claim 1, characterized in that, The specific surface area of ​​the composite aerogel is 400-1200 m². 2 / g, with a room temperature thermal conductivity of less than 0.015 W / (m·K).

5. A method for preparing a ceramic-based nanosheet / nanowire composite aerogel, characterized in that, Includes the following steps: (1) Disperse inorganic nanoparticles in a solvent, add a certain proportion of catalyst, and stir rapidly at room temperature for 6-10 hours at a speed of 3000-8000 rpm until a homogeneous, non-settling inorganic nanoparticle dispersion is formed; the catalyst is any one of acetic acid, hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid. (2) Add a metal source to the inorganic nanoparticle dispersion obtained in step (1), and stir under pressure in a desorption bath for 4-8 hours to obtain a homogeneous inorganic precursor solution; the desorption bath refers to the mixture after adding the metal source to the inorganic nanoparticle dispersion. (3) The inorganic precursor solution obtained in step (2) is placed in a hydrothermal reactor to synthesize an inorganic nanowire wet gel, wherein the metal source is uniformly distributed in the interior and outer surface of the entire nanowire. (4) Place the inorganic nanowire wet gel obtained in step (3) in a displacement bath, add a certain amount of crosslinking agent, and after completing 3-5 solvent displacement treatments, place the inorganic nanowire wet gel in liquid nitrogen for rapid freezing treatment, and then obtain inorganic nanowire aerogel through supercritical drying process; the crosslinking agent is one of methyltrimethoxysilane, methyltriethoxysilane, tetra-n-butoxysilane, trimethylmethoxysilane, or tetraethyl orthosilicate; the displacement bath is a low surface tension solvent, which is one or a combination of at least two of benzene, toluene, n-hexane, cyclohexane, diethyl ether, acetone, dichloromethane, or ethyl acetate, and its surface tension is less than 30 mN / m; (5) The inorganic nanowire aerogel obtained in step (4) is subjected to ammonia vapor fumigation treatment, and then placed in a vacuum oven at a temperature of 80-130℃ for 4-8 hours to react. The aerogel after fumigation treatment undergoes chemical co-precipitation reaction with metal source ions under thermal induction environment, and nanosheets are vertically grown in situ from the inside to the outside at the confined area of ​​the nanowire. Finally, after high-temperature heat treatment, ceramic-based nanosheet / nanowire composite aerogel is obtained. The ceramic-based nanosheet / nanowire composite aerogel is one or a combination of at least two of SiO2-based, TiO2-based, ZrO2-based, and Al2O3-based aerogel.

6. The method according to claim 5, characterized in that, The inorganic nanoparticles in step (1) are any one of silicon dioxide, titanium dioxide, zirconium dioxide, and aluminum oxide; the solvent is any one or a mixture of at least two of water, ethanol, ethylene glycol, propylene glycol, isopropanol, tert-butanol, benzyl alcohol, and diacetone alcohol; and the mass concentration of the resulting inorganic nanoparticle dispersion is 10-45%.

7. The method according to claim 5, characterized in that, The metal source in step (2) is any one of titanium, zirconium and aluminum; the mass ratio of the metal source to the inorganic nanoparticles is 1:5 to 1:20; the molar concentration of the inorganic acid in the desorption bath is 0.1-5 mol / L; the desorption bath is pressurized and stirred, wherein the desorption pressure is 1-4 MPa and the desorption temperature is 80-150℃.

8. The method according to claim 5, characterized in that, The hydrothermal reaction conditions in step (3) are: reaction temperature 150-300℃, reaction time 6-24h, reaction pressure 2-10MPa; and the mass concentration of the crosslinking agent is 0.5-5%.

9. The method according to claim 5, characterized in that, The conditions for ammonia vapor fumigation in step (5) are: ammonia vapor flow rate 20~80m / s, fumigation temperature 20-40℃, fumigation time 1-5h; the conditions for high-temperature heat treatment are: heating rate 2-10℃ / min, calcination temperature 600-1400℃, calcination time 8-20h, and heat preservation time 1-4h.

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