CN113416054B - Preparation method of silica nanofiber/MXene composite aerogel with double protection performance - Google Patents
Preparation method of silica nanofiber/MXene composite aerogel with double protection performance Download PDFInfo
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Abstract
Silica nanofiber/MXene composite aerogel with double protection performanceThe preparation method belongs to the field of heat preservation and insulation materials. The flexible heat-insulation support of the aerogel is formed by taking the flexible silica nano fiber as a template, and the sheet material MXene is used as a rigid support, so that the mechanical strength of the fiber aerogel is improved, and the aerogel is endowed with conductivity. SiO2 2 the/MXene aerogel exhibited good resilience to compression both after 100 cycles at 50% strain and after 100 cycles at high strain 90%. The high-efficiency heat insulation protection effect is achieved when the temperature is lower than 400 ℃, and the thermal conductivity at 25 ℃ is as low as 21mW m ‑1 K ‑1 4mW m lower than the thermal conductivity of air ‑1 K ‑1 (ii) a When the temperature is lower than 400 ℃, instantaneous circuit fusing occurs, and high-temperature/fire early warning protection is realized.
Description
The technical field is as follows:
the invention belongs to the field of heat insulation materials, and relates to a nanofiber composite aerogel material.
Background art:
thermal energy plays a crucial role in supporting living systems and controlling various industrial processes. Thermal insulation materials, which are one of materials capable of managing thermal energy, have a wide range of applications in various fields. The emerging fields of intelligent human and industrial systems place new demands on the physical properties of these materials. They should be flexible to withstand mechanical deformation, have repeatable compressibility, etc. to suit the application. Compared with traditional thermal insulation materials (such as mineral wool, expanded polystyrene and polyurethane), silica aerogel has inherent low density and mesoporous structure and low thermal conductivity coefficient, and becomes a thermal insulation material with great development prospect at present. Common silica aerogels are characterized by an open porous structure whose framework consists of interconnected silica nanoparticles. However, silica aerogels generally have brittle properties, low mechanical strength and poor flexibility due to weak interfacial interactions between nanoparticles, limiting their widespread use. The development of aerogel materials with good mechanical strength and high flexibility is promising in market application.
At present, the common methods for improving the mechanical properties of inorganic silica aerogels are as follows: i) the flexible silica nanofiber is prepared by an electrostatic spinning method, so that a pearl chain-shaped brittle structure is reduced, but the pure silica nanofiber aerogel is too flexible and lacks of mechanical strength; ii) use of organosiloxanes to provide aerogels with compressive elasticity, inevitably increasing the density of the aerogel, reducing its ability to recover from deformation; and iii) incorporating the two-dimensional lamellar material into the silica aerogel to exert a synergistic effect to toughen the aerogel. Among other things, the fiber-reinforced method allows the elastic modulus of the composite aerogel to be adjusted over many orders of magnitude and provides the final product with the ability to sustain bending and even folding deformations. This increase in mechanical strength is due to hydroxyl (-OH) groups in the fiber, whose nano-fibrils can strongly interact with other materials via hydrogen or siloxane bonds. This strong interfacial interaction is accompanied by a 3D interconnected fiber network, resulting in a composite aerogel with improved mechanical strength.
For the study of nanocomposites with structural robustness and multiple additional functions, there is a need to combine hard and soft components into a natural material with a layered structure spanning a range of different lengths. The rigid members, being the blocks, provide stiffness to the material, while the soft members provide ductility to the material that dissipates energy under mechanical deformation. The binary cooperation principle is applied to design of a heterogeneous network, and the 'hard-soft' binary cooperation composite aerogel with high flexibility and excellent heat insulation performance is designed. Meanwhile, considering the application environment of the heat insulating material, the possibility of fire is inevitably increased, and therefore, the heat insulating material is combined with a circuit to be designed into an electronic device with a fire early warning function. Specifically, a flexible support of the aerogel is formed by using the flexible silica nanofiber as a template, and MXene serving as a conductive sheet material is used as a rigid support to improve the mechanical strength of the fiber aerogel, so that the ultra-elastic and ultra-light silica nanofiber/MXene composite aerogel is obtained. The aerogels exhibited good resilience to compression both 100 cycles at 50% strain and 100 cycles at high strain of 90%. SiO at 25 DEG C 2 The thermal conductivity of the/MX-1 is 21mW m -1 K -1 4mW m lower than the thermal conductivity of air -1 K -1 Has good heat preservation and insulation performance. Meanwhile, the hybrid aerogel is connected with a circuit, can be used as a fire alarm to have instant response performance to fire, and is expected to have a great application prospect in the aspect of fire early-warning devices.
The invention content is as follows:
the invention aims to provide a preparation method of silicon dioxide nanofiber/MXene composite aerogel with double protection functions of heat insulation and fire early warning.
The technical scheme of the invention is as follows:
the silica nanofiber/MXene composite aerogel with double protection performance is characterized by being composed of silica nanofibers and two-dimensional MXene, the SiO2 nanofibers with high length-diameter ratio are intertwined with one another and assembled into an interconnected heat insulation framework, and the rich oxygen-containing functional groups on the surface of the MXene nanosheets and the SiO 2 The SiO and the SiO are tightly combined and enhanced through the interaction of hydrogen bonds and the like 2 Structural stability of the skeleton.
Further preferably, the integral structure of the silica nanofiber/MXene composite aerogel is a honeycomb structure with unidirectional micro-channels, and the honeycomb structure also has mesopores.
The preparation method of the silica nanofiber/MXene composite aerogel with double protection performance is characterized by comprising the following steps: the silicon dioxide nanofiber/MXene composite aerogel prepared by using the liquid nitrogen-assisted directional freeze-drying technology has anisotropic mechanical property, heat insulation and preservation property and high length-diameter ratio 2 The nano-fibers are mutually entangled and assembled into an interconnected heat insulation framework, and the MXene nano-sheet has rich oxygen-containing functional groups and SiO on the surface 2 The SiO and the SiO are tightly combined and enhanced through the interaction of hydrogen bonds and the like 2 The structural stability of the framework and the proper conductivity of the aerogel are realized, so that the hybrid aerogel is endowed with high-temperature early warning performance.
The preparation method of the silica nanofiber/MXene composite aerogel with double protection performance is characterized by comprising the following steps:
(1) preparation of SiO 2 Nano-fiber
SiO 2 The preparation method of the nanofiber is a sol-gel electrospinning method; first, tetraethyl orthosilicate (TEOS), H 3 PO 4 And water in a molar ratio of 1:0.01:11, stirring and mixing at room temperature for 10-20 h to obtain a silicon precursor sol solution. PVA is dissolved in Deionized Water (DW) at 90 ℃ and stirred for 3-8 h to prepare 8wt% -12 wt% PVA water solution; then, mixing the silica sol and the PVA solution according to different mass ratios (2: 1-1: 2), and fully stirring and mixing for 3-8 h to obtain an electrospinning precursor solution; front body fluid is injected into a 10mL needle tube, and a No. 18-22 stainless steel electrospinning special needle is selected as the needle. Injecting at a speed of 1-2 mL h -1 And carrying out electrostatic spinning under the conditions that the distance between a collector and the electrostatic spinning is 10-20 cm and the voltage is 8-20 kV. Collecting PVA/TEOS composite nano-fiber in a tube furnace at 2-7 ℃ for min -1 The temperature is raised to 700-900 ℃ at the temperature raising speed. Calcining the mixture in air at the temperature for 1 to 4 hours to remove the PVA template, and obtaining pure SiO 2 A nanofiber;
(2) preparation of MXene nanosheet
1 part by mass of LiF was dissolved in 9 mol. L -1 Adding 1 part by mass of Ti into HCl under stirring 3 AlC 2 Powder; reacting the obtained mixture at 30-35 ℃ for 20-30 hours to obtain MXene (Ti) 3 C 2 ) Repeatedly washing the suspension with deionized water, and centrifuging at 3000-5000 rpm for 5-10 minutes until the pH value reaches 6; finally, carrying out ultrasonic treatment on the MXene suspension for 1-2 hours under argon gas flow, wherein the gas flow rate is 30-60 mL/min -1 Centrifuging at 3000-5000 rpm for 1-2 hours to obtain a uniform supernatant with MXene tablets; freeze drying in freeze dryer to obtain MXene (Ti) 3 C 2 ) Nanosheets.
(3) Preparation of SiO 2 nanofiber/MXene aerogels
First, according to SiO 2 The mass ratio of the nano fiber to MXene is 1:0 or 0:1 or 1-3: 1, and SiO is 2 The mass ratio of the nano-fiber to the PVP is 2-6: 1, MXene nanosheets are dispersed in water, and then SiO is added in sequence 2 And homogenizing the nano-fibers and PVP for 20-40 minutes at 8000-12000 rpm by a homogenizer to obtain uniformly dispersed suspension. Then magnetically stirring the dispersion liquid for 15-30 minutes and carrying out ultrasonic treatment for 30-60 minutes; treating the dispersion by directional freezing technology or random freezing technology, freeze-drying in a vacuum freeze-drying machine at a temperature below-50 deg.C and a pressure below 20Pa for more than 48h to obtain SiO 2 nanofiber/MXene aerogel.
And (3) adopting an ice template directional freezing technology, namely vertically placing a copper column in a container filled with liquid nitrogen, placing a square mould with heat insulation at other parts and only bottom heat conduction on the copper column, adding the dispersion into the mould placed on the copper column, inducing the directional growth of ice crystals from the bottom end to the top end by depending on the temperature difference between the bottom end of the mould (liquid nitrogen temperature) and the top end of the mould (room temperature), and finishing the directional freezing process when the upper-layer dispersion in the mould is completely frozen.
Electrostatic spinning prepared SiO 2 The average diameter of the nanofibers was 300 nm; the monolithic layer thickness of MXene nanosheets was 1.59nm (close to its theoretical thickness of 1 nm).
Directionally frozen SiO 2 After the MX-1 aerogel is subjected to 50% compressive strain cycle for 100 times, the recovery rate is still high, the stress retention rate reaches 97.3%, and the maximum compressive strain of the MX-1 aerogel can reach 90%. SiO frozen at will 2 After 100 cycles of 50% compressive strain,/MX-I, the stress retention rate remained only 72.1%.
The thermal conductivity of the composite aerogel is as low as 21mW m at room temperature of 25 DEG C -1 K -1 Thermal conductivity of 25mW m lower than that of air -1 K -1 Has good heat insulation performance.
SiO 2 The nano fiber/MXene composite aerogel can still keep a proper far-end temperature and has good high-temperature heat insulation/low-temperature heat preservation performance when being placed in a high-temperature environment at 300 ℃ for 30min or in a cold environment at the temperature of less than minus 30 ℃ for 30 min. Can be used at the temperature of-30 ℃ to 300 ℃.
The invention relates to 3 basic principles:
(1) the addition of MXene, a two-dimensional material with rich surface active sites, can fully exert the synergistic effect of the one-dimensional material and the two-dimensional material to construct the 3D aerogel with a stable structure and endow the aerogel with good elasticity.
(2) Double protection performance: the high-conductivity MXene is oxidized into non-conductive TiO under the condition that the temperature is higher than 400 DEG C 2 . Therefore, when the temperature is less than 400 ℃, the composite aerogel plays a first heavy protection role-separationAnd (4) heat preservation. When the temperature is higher than 400 ℃, the composite aerogel plays a second protection role, namely the circuit is fused, and early warning is triggered.
(3) The directional freezing principle: the directional freezing is carried out at ultra-low temperature supplied by liquid nitrogen, and in the process, a plurality of ice crystals are from SiO 2 Bottom start and vertical growth of nanofiber/MXene suspension, SiO 2 The nanofibers and MXene sheets were expelled by a plurality of icicles to form vertically oriented SiO 2 the/MXene structure. Finally, the icicles are sublimated by freeze-drying to form anisotropic SiO with unidirectional microchannels 2 the/MXene aerogel.
Drawings
Fig. 1 is a flow chart of preparation of silica nanofiber/MXene composite aerogel.
FIG. 2 a b c are SiO 2 SEM photograph of nanofibers; TEM photograph of MXene nanosheets; AFM photograph of MXene nanoplatelets.
FIG. 3 is SiO 2 SEM photograph of oriented structure of/MX composite aerogel.
FIG. 4a b c d shows examples 4 (SiO) 2 /MX-3), example 5 (SiO) 2 /MX-2), example 6 (SiO) 2 /MX-1), example 8 (A-SiO) 2 ) Density of example 9(A-MX) (FIG. 4 a); porosity (fig. 4 b); mesoporous structure (fig. 4 c); average pore size (fig. 4 d).
FIG. 5 shows example 6 (SiO) 2 /MX-1), example 8 (A-SiO) 2 ) Example 9(A-MX) thermogravimetric curves under air atmosphere.
FIG. 6 a b c d shows example 6 (SiO) 2 MX-1) stress-strain plot in 50% compression; example 5 (SiO) 2 MX-2) stress-strain plot in 50% compression; example 4 (SiO) 2 /MX-3) stress-strain plot for 50% compression; example 10 (SiO) 2 /MX-I) stress-strain plot of 50% compression.
FIG. 7 shows example 6 (SiO) 2 /MX-1) stress-strain diagram at high compressive strain of 90%;
FIG. 8 a b shows the results of example 4 (SiO) 2 /MX-3), example 5 (SiO) 2 /MX-2), example 6 (Si)O 2 /MX-1), example 8 (A-SiO) 2 ) Example 9(a-MX) thermal conductivity at 25 ℃; taking example 6 as an example, (SiO) 2 the/MX-1) composite aerogel has anisotropic thermal conductivity.
FIG. 9a b shows examples 6 (SiO) 2 /MX-1) before (FIG. 9a) and after (FIG. 9b) exposure to a high temperature of 400 ℃.
FIG. 10a shows the structure of example 6 (SiO) 2 /MX-1) as an example, the radial insulation mechanism of the aerogel on a 300 ℃ hot stage; b d c are respectively radial SiO 2 Placing the/MX-1 aerogel on a 300 ℃ hot bench for 0min, 15min and 30min of infrared thermal imaging pictures.
FIG. 11a shows the structure of example 6 (SiO) 2 PerMX-1) as an example, a radial heat preservation mechanism of aerogel on a copper column soaked by liquid nitrogen; b d c are respectively radial SiO 2 Placing the/MX-1 aerogel on a 300 ℃ hot bench for 0min, 15min and 30min of infrared thermal imaging pictures.
Detailed Description
The present invention will be further described in the following examples, which are illustrative, not restrictive and are not intended to limit the scope of the invention.
Example 1.
Firstly, preparing SiO 2 Nanofibers prepared by reacting TEOS and H 3 PO 4 And water in a molar ratio of 1:0.01:11, stirring and mixing for 10 hours at room temperature to obtain a silicon precursor sol solution. The 8 wt% PVA aqueous solution was prepared by dissolving PVA in Deionized Water (DW) at 90 ℃ and stirring for 3 hours. And then, mixing the silica sol and the PVA solution according to the mass ratio of 2:1, and fully stirring and mixing for 3h to obtain the electrospun precursor solution. Front body fluid is injected into a 10mL needle tube, and an 18-grade stainless steel electro-spinning special needle is selected as the needle. At a bolus rate of 1mL h -1 And electrostatic spinning is carried out under the conditions that the distance between a collector and the electrode is 10cm and the voltage is 8 kV. Collecting PVA/TEOS composite nano fiber in a tube furnace at 2 deg.C for min -1 The temperature rising speed is increased to 700 ℃ for heat treatment. Calcining the mixture for 1 hour in the air at the temperature to obtain SiO 2 And (3) nano fibers.
MXene nanosheets were prepared by dissolving 1 part of LiF in 9 mol. L -1 HCl, then 1 part of Ti is added slowly with stirring 3 AlC 2 And (3) powder. The resulting mixture was reacted at 35 ℃ for 20 hours to give an MXene suspension, which was repeatedly washed with deionized water and centrifuged at 3000rpm for 5 minutes until its pH reached 6. Finally, the MXene suspension was sonicated under argon flow for 1 hour at a gas flow rate of 30mL min -1 And centrifuged at 3000rpm for 1 hour to obtain a uniform supernatant with MXene pellet. Freezing the MXene nano-sheet, and then freezing and drying the MXene nano-sheet in a freeze dryer to obtain the MXene nano-sheet.
Finally, preparing SiO 2 Nano fiber/MXene composite aerogel according to SiO 2 The mass ratio of the mixed solution to MXene is 3:1, SiO 2 The mass ratio of MXene nanosheets to PVP is 2:1, MXene nanosheets are dispersed in water, and SiO is sequentially added 2 The nano-fiber, PVP and homogenized for 20 minutes by a homogenizer at 8000rpm to obtain a uniformly dispersed suspension. Subsequently, the dispersion was magnetically stirred for 15 minutes and sonicated for 30 minutes. The method comprises the following steps of putting a copper column in a container filled with liquid nitrogen, putting a mould with the rest parts being heat-insulated and only the bottom end being heat-conductive on the copper column, adding the dispersion into the mould placed on the copper column, and finishing the directional freezing process when the upper layer of dispersion in the mould is completely frozen. The prepared directional frozen SiO 2 Freeze drying the nanometer fiber/MXene in a freeze dryer at the temperature below 50 ℃ below zero and under the pressure of 20Pa for more than 48h to obtain SiO 2 nanofiber/MXene composite aerogel.
Example 2.
Firstly, preparing SiO 2 Nano-fiber prepared from TEOS and H 3 PO 4 And water in a molar ratio of 1:0.01:11, stirring and mixing at room temperature for 20 hours to obtain a silicon precursor sol solution. The 12 wt% PVA aqueous solution was prepared by dissolving PVA in Deionized Water (DW) at 90 ℃ and stirring for 8 hours. And then, mixing the silica sol and the PVA solution according to the mass ratio of 1:2, and fully stirring and mixing for 8 hours to obtain the electrospun precursor solution. Front body fluid is injected into a 10mL needle tube, and a No. 22 stainless steel electrospinning special needle is selected as the needle. At a bolus rate of 2mL h -1 Collector distance 20cm, voltage 20kVAnd carrying out electrostatic spinning under the conditions. And (3) depositing and collecting the electrospun PVA/TEOS composite nano-fibers on tin foil paper. Finally, the collected PVA/TEOS composite nano-fiber is put in a tube furnace for 7 ℃ min -1 The temperature rise speed is increased to 900 ℃ for heat treatment. Calcining the mixture for 4 hours in the air at the temperature to obtain pure SiO 2 And (3) nano fibers.
MXene nanoplatelets were prepared as in example 1 except that the mixture was changed to react at 30 ℃ for 30 hours.
Finally, preparing SiO 2 Nano fiber/MXene composite aerogel according to SiO 2 The mass ratio of the mixed solution to MXene is 1:1, and SiO is 2 The mass ratio of MXene nano-sheets to PVP is 6:1, MXene nano-sheets are dispersed in water, and SiO is sequentially added 2 PVP, and homogenizing at 12000rpm for 40 min by a homogenizer to obtain a uniformly dispersed suspension. Subsequently, the dispersion was magnetically stirred for 30 minutes and sonicated for 60 minutes. The method comprises the following steps of putting a copper column in a container filled with liquid nitrogen, putting a mould with the rest parts being heat-insulated and only the bottom end being heat-conductive on the copper column, adding the dispersion into the mould placed on the copper column, and finishing the directional freezing process when the upper layer of dispersion in the mould is completely frozen. The prepared directional frozen SiO 2 Freeze drying the nano fiber/MXene in a freeze dryer at the temperature below-50 ℃ and the pressure below 20Pa for more than 48h to obtain SiO 2 nanofiber/MXene composite aerogel.
Example 3.
Firstly, preparing SiO 2 Nano-fiber prepared from TEOS and H 3 PO 4 And water in a molar ratio of 1:0.01:11, stirring and mixing for 15h at room temperature to obtain a silicon precursor sol solution. A10 wt% aqueous PVA solution was prepared by dissolving PVA in Deionized Water (DW) at 90 ℃ and stirring for 5 hours. And then, mixing the silica sol and the PVA solution according to the mass ratio of 1:1, and fully stirring and mixing for 6 hours to obtain the electrospun precursor solution. Front body fluid is injected into a 10mL needle tube, and a No. 20 stainless steel electrospinning special needle is selected as the needle. The injection speed is 1.5mL h -1 Electrostatic spinning is carried out under the conditions that the distance between a collector and the electrode is 14cm and the voltage is 11 kV. PVA/TEOS composite nano fiber deposition collection after electric spinningOn a tin foil paper. Finally, the collected PVA/TEOS composite nano-fiber is put in a tube furnace for 5 ℃ min -1 The temperature rising speed is increased to 800 ℃ for heat treatment. Calcining in air at the temperature for 2h, removing the PVA template to obtain pure SiO 2 And (3) nano fibers.
MXene nanoplatelets were prepared as in example 2.
Finally, preparing SiO 2 Nano fiber/MXene composite aerogel according to SiO 2 The mass ratio of the mixed solution to MXene is 2:1, SiO 2 The mass ratio of MXene nano-sheets to PVP is 4:1, MXene nano-sheets are dispersed in water, and SiO is sequentially added 2 PVP, and homogenized by a homogenizer at 10000rpm for 30 minutes to give a uniformly dispersed suspension. The dispersion was subjected to directional freezing treatment to prepare an oriented structure in the same manner as in example 1.
Example 4.
Preparation of SiO 2 Preparation of nanofiber and MXene nanosheet as in example 3, and finally preparation of SiO 2 /MXene composite aerogel, according to SiO 2 The mass ratio of the mixed solution to MXene is 3:1, SiO 2 The mass ratio of MXene nano-sheets to PVP is 5:1, MXene nano-sheets are dispersed in water, and SiO is sequentially added 2 PVP and a homogenizer at 10000rpm for 20 minutes to obtain a uniformly dispersed suspension. The dispersion was subjected to directional freezing treatment to prepare an oriented structure in the same manner as in example 1.
Aerogels prepared by this example, having densities as low as 4.21mg cm -3 The porosity is 99.76%, the obvious mesoporous distribution is realized, and the average pore diameter is 23.43 nm; after 100 cycles of 50% compressive strain, plastic deformation reaches 22%; the thermal conductivity of the heat-insulating material is 24mW m at 25 DEG C -1 K -1 。
Example 5.
Preparation of SiO 2 Nanofibers as in example 3
MXene nanosheets were prepared by dissolving 1 part of LiF in 9 mol. L -1 HCl, then 1 part of Ti is added slowly with stirring 3 AlC 2 And (3) powder. The resulting mixture was reacted at 35 ℃ for 30 hours to give MXene suspension, which was repeatedly washed with deionized water and washed with deionized waterCentrifuge at 4000rpm for 5 minutes until its pH reaches 6. Finally, the MXene suspension was sonicated under argon flow for 1 hour at a gas flow rate of 60mL min -1 And centrifuged at 5000rpm for 1 hour to obtain a homogeneous supernatant with MXene pellet. Freezing the MXene nanosheet, and then freeze-drying the MXene nanosheet in a freeze dryer to obtain the MXene nanosheet.
Finally, preparing SiO 2 the/MXene composite aerogel, as in example 4, was modified by SiO alone 2 The mass ratio of MXene to MXene was 2: 1.
Aerogels prepared by this example, having densities as low as 5.14mg cm -3 The porosity is 99.64 percent, the obvious mesoporous distribution is realized, and the average pore diameter is 15.93 nm; after 100 cycles of 50% compressive strain, plastic deformation reaches 17%; the thermal conductivity of the heat-insulating material is 28mW m at 25 DEG C -1 K -1 。
Example 6
Preparation of SiO 2 The nanofiber and MXene nanosheet were prepared as in example 5.
Finally, preparing SiO 2 PerMXene composite aerogel, as in example 5, only SiO was varied 2 The mass ratio of MXene to MXene was 1: 1.
Aerogels prepared by this example, having densities as low as 5.68mg cm -3 The porosity is 99.40%, the obvious mesoporous distribution is realized, and the average pore diameter is 18.22 nm; after 50% compressive strain is cycled for 100 times, the recovery rate is still high, the stress retention rate reaches 97.3%, the plastic deformation is only 1%, and the maximum compressive strain can reach 90%; the radial thermal conductivity of the heat-insulating material is as low as 21mW m at 25 DEG C -1 K -1 Axial thermal conductivity of 27mW m -1 K -1 。
Example 7
Preparation of SiO 2 Preparation of nanofiber and MXene nanosheet As in example 5, and finally preparation of SiO 2 /MXene composite aerogel, according to SiO 2 The mass ratio of the mixed solution to MXene is 3:1, SiO 2 The mass ratio of MXene nanosheets to PVP is 3:1, MXene nanosheets are dispersed in water, and SiO is sequentially added 2 PVP, and homogenizing for 20 minutes at 12000rpm by a homogenizer to obtain uniformly dispersed suspensionAnd (4) liquid. Subsequently, the dispersion was magnetically stirred for 25 minutes and sonicated for 25 minutes. The dispersion was subjected to directional freezing treatment to prepare an oriented structure in the same manner as in example 1.
Example 8.
Preparation of SiO 2 Nanofibers as in example 3
Finally, preparing SiO 2 Aerogel, according to SiO 2 The mass ratio of the suspension to PVP is 5:1, and the suspension is homogenized by a homogenizer at 10000rpm for 20 minutes to obtain a uniformly dispersed suspension. Subsequently, the dispersion was magnetically stirred for 15 minutes and sonicated for 30 minutes. The dispersion was subjected to directional freezing treatment to prepare an oriented structure in the same manner as in example 1.
Aerogels prepared by this example, having densities as low as 3.86mg cm -3 The porosity is 99.86%, the obvious mesoporous distribution is realized, and the average pore diameter is 25 nm. The thermal conductivity of the heat-insulating material at 25 ℃ is 27mW m -1 K -1 。
Example 9.
MXene nanoplatelets were prepared as in example 2.
And finally, preparing MXene aerogel, and homogenizing the suspension of MXene and PVP for 20 minutes by a homogenizer at 10000rpm according to the mass ratio of 5:1 to obtain a uniformly dispersed suspension. Subsequently, the dispersion was magnetically stirred for 15 minutes and sonicated for 30 minutes. The dispersion was subjected to directional freezing treatment to prepare an oriented structure in the same manner as in example 1.
Aerogels prepared by this example, having densities as low as 6.75mg cm -3 The porosity is 99.82%, the obvious mesoporous distribution is realized, and the average pore diameter is 20 nm. The thermal conductivity of the heat-insulating material used at 25 ℃ is 32mW m -1 K -1 。
Example 10
Preparation of SiO 2 The nanofiber and MXene nanosheet were prepared as in example 5.
Finally, preparing SiO 2 /MXene composite aerogel, according to SiO 2 The mass ratio of the mixed solution to MXene is 1:1, and SiO is 2 The mass ratio of MXene nano-sheets to PVP is 5:1, MXene nano-sheets are dispersed in water, and SiO is sequentially added 2 PVP, and homogenized by a homogenizer at 10000rpm for 20 minutes to obtain a uniformly dispersed suspension. The suspension is optionally frozen to obtain a composite aerogel of any structure by magnetically stirring the dispersion for 15 minutes and sonicating for 30 minutes. Directly pouring the suspension into a mould, and putting the mould into a refrigerator at the temperature of 80 ℃ below zero for freezing. Optionally freezing the obtained SiO 2 Freeze drying the nanometer fiber/MXene in a freeze dryer at the temperature below 50 ℃ below zero and under the pressure of 20Pa for more than 48h to obtain SiO 2 nanofiber/MXene composite aerogels.
The aerogel prepared by this example had a stress retention of 72.1% after 100 cycles of 50% compressive strain.
Under the same conditions, with SiO 2 The mass ratio of the nano-fiber to MXene is changed from 3:1 to 2:1 to 1:1, and the composite aerogel has ultralow density of 4.21mg cm -3 、5.14mg cm -3 、5.68mg cm -3 。
Under the same conditions, with SiO 2 The mass ratio of the nano fibers to the MXene is changed from 3:1 to 2:1 to 1:1, and the composite aerogel has ultrahigh porosity of 99.76%, 99.64% and 99.40% respectively.
Under the same conditions, with SiO 2 The mass ratio of the nano fiber to MXene is changed from 3:1 to 2:1 to 1:1, the composite aerogel has rich mesoporous structures, and the average pore diameters are 23.43nm, 15.93nm and 18.22nm respectively.
Under the same conditions, with SiO 2 The mass ratio of the nano-fiber to MXene is changed from 3:1 to 2:1 to 1:1, and after 100 cycles of the composite aerogel under 50% strain, the composite aerogel respectively has 22%, 17% and 1% of plastic deformation.
Claims (9)
1. The silica nanofiber/MXene composite aerogel with double protection performances is characterized by being composed of silica nanofibers and two-dimensional MXene, and having a high length-diameter ratio of SiO 2 The nano-fibers are mutually entangled and assembled into an interconnected heat insulation framework, and the MXene nano-sheet has rich oxygen-containing functional groups and SiO on the surface 2 Connecting between two adjacent roomsSiO tightly combined and enhanced through hydrogen bond interaction 2 Structural stability of the framework; the preparation method comprises the following steps:
the silicon dioxide nanofiber/MXene composite aerogel prepared by using the liquid nitrogen-assisted directional freeze-drying technology has anisotropic mechanical property, heat insulation and preservation property and high length-diameter ratio 2 The nano-fibers are mutually entangled and assembled into a mutually connected heat insulation framework, and the MXene nanosheet is rich in oxygen-containing functional groups and SiO 2 The SiO and the silicon dioxide are tightly combined and enhanced through hydrogen bond interaction 2 The framework has stable structure, and the aerogel has proper conductivity so as to endow the hybrid aerogel with high-temperature early warning performance;
the preparation process comprises the following steps:
(1) preparation of SiO 2 Nano-fiber
SiO 2 The preparation method of the nanofiber is a sol-gel electrospinning method; first, tetraethyl orthosilicate (TEOS), H 3 PO 4 Stirring and mixing the silicon precursor sol with water at a molar ratio of 1:0.01:11 at room temperature for 10-20 h to obtain a silicon precursor sol solution; dissolving PVA in deionized water DW at 90 ℃ and stirring for 3-8 h to prepare PVA water solution with 8-12 wt%; then, mixing the silica sol and the PVA solution according to different mass ratios of 2: 1-1: 2, and fully stirring and mixing for 3-8 h to obtain an electrospinning precursor solution; injecting front body fluid into a 10mL needle tube, wherein a No. 18-22 stainless steel electrospinning special needle is selected as the needle; the injection speed is 1-2 mL h -1 Carrying out electrostatic spinning under the conditions that the distance between a collector and the collector is 10-20 cm and the voltage is 8-20 kV; collecting PVA/TEOS composite nano-fiber in a tube furnace at 2-7 ℃ for min -1 The temperature rise speed is to rise the temperature to 700-900 ℃; calcining the mixture in air at the temperature for 1 to 4 hours to remove the PVA template, and obtaining pure SiO 2 A nanofiber;
(2) preparation of MXene nanosheet
1 part by mass of LiF was dissolved in 9 mol. L -1 Adding 1 part by mass of Ti into HCl and slowly adding the mixture under stirring 3 AlC 2 Powder; the obtained mixture reacts for 20 to 30 hours at a temperature of between 30 and 35 ℃ to obtain MXene Ti 3 C 2 Suspending the solution in deionized waterWashing, and centrifuging at 3000-5000 rpm for 5-10 minutes until the pH value reaches 6; finally, carrying out ultrasonic treatment on the MXene suspension for 1-2 hours under argon gas flow, wherein the gas flow rate is 30-60 mL/min -1 Centrifuging at 3000-5000 rpm for 1-2 hours to obtain a uniform supernatant with MXene tablets; freeze-drying in a freeze dryer to obtain MXene nanosheets;
(3) preparation of SiO 2 nanofiber/MXene aerogels
First, according to SiO 2 The mass ratio of the nano fiber to MXene is 1:0 or 0:1 or 1-3: 1, and SiO is 2 The mass ratio of the nano-fiber to the PVP is 2-6: 1, MXene nanosheets are dispersed in water, and then SiO is added in sequence 2 Homogenizing the nano-fibers and PVP for 20-40 minutes at 8000-12000 rpm by a homogenizer to obtain uniformly dispersed suspension; then magnetically stirring the dispersion liquid for 15-30 minutes and carrying out ultrasonic treatment for 30-60 minutes; treating the dispersion by directional freezing technology or random freezing technology, freeze-drying in a vacuum freeze-drying machine at a temperature below-50 deg.C and a pressure below 20Pa for more than 48h to obtain SiO 2 nanofiber/MXene aerogel.
2. The silica nanofiber/MXene composite aerogel with dual barrier properties according to claim 1, wherein the monolithic structure of the silica nanofiber/MXene composite aerogel is a honeycomb structure with unidirectional micro-channels, and the honeycomb structure has mesopores.
3. The preparation method of the silica nanofiber/MXene composite aerogel with dual-protection performance of claim 1, wherein the preparation method comprises the following steps: the silicon dioxide nanofiber/MXene composite aerogel prepared by using the liquid nitrogen-assisted directional freeze-drying technology has anisotropic mechanical property, heat insulation and preservation property and high length-diameter ratio 2 The nano-fibers are mutually entangled and assembled into an interconnected heat insulation framework, and the MXene nano-sheet has rich oxygen-containing functional groups and SiO on the surface 2 The SiO and the silicon dioxide are tightly combined and enhanced through hydrogen bond interaction 2 Structure of skeletonThe stability is ensured, and the aerogel has proper conductivity so as to endow the hybrid aerogel with high-temperature early warning performance;
the preparation process comprises the following steps:
(2) preparation of SiO 2 Nano-fiber
SiO 2 The preparation method of the nanofiber is a sol-gel electrospinning method; first, tetraethyl orthosilicate (TEOS), H 3 PO 4 Stirring and mixing the silicon precursor sol with water at a molar ratio of 1:0.01:11 at room temperature for 10-20 h to obtain a silicon precursor sol solution; dissolving PVA in deionized water DW at 90 ℃ and stirring for 3-8 h to prepare PVA aqueous solution with the concentration of 8-12 wt%; then, mixing the silica sol and the PVA solution according to different mass ratios of 2: 1-1: 2, and fully stirring and mixing for 3-8 h to obtain an electrospinning precursor solution; injecting front body fluid into a 10mL needle tube, and selecting a No. 18-22 stainless steel electro-spinning special needle from the needles; injecting at a speed of 1-2 mL h -1 Carrying out electrostatic spinning under the conditions that the distance between a collector and the collector is 10-20 cm and the voltage is 8-20 kV; collecting PVA/TEOS composite nano-fiber in a tube furnace at the temperature of 2-7 ℃ for min -1 The temperature rise speed is that the temperature is raised to 700-900 ℃; calcining the mixture in air at the temperature for 1 to 4 hours to remove the PVA template, and obtaining pure SiO 2 A nanofiber;
(2) preparation of MXene nanosheet
1 part by mass of LiF was dissolved in 9 mol. L -1 Adding 1 part by mass of Ti into HCl under stirring 3 AlC 2 Powder; reacting the obtained mixture at 30-35 ℃ for 20-30 hours to obtain MXene Ti 3 C 2 Repeatedly washing the suspension with deionized water, and centrifuging at 3000-5000 rpm for 5-10 minutes until the pH value reaches 6; finally, carrying out ultrasonic treatment on the MXene suspension for 1-2 hours under argon gas flow, wherein the gas flow rate is 30-60 mL/min -1 Centrifuging at 3000-5000 rpm for 1-2 hours to obtain a uniform supernatant with MXene tablets; freeze-drying in a freeze dryer to obtain MXene nanosheets;
(3) preparation of SiO 2 nanofiber/MXene aerogels
First, according to SiO 2 The mass ratio of the nano fiber to MXene is 1:0 or 0:1 or 1-3: 1, and SiO is 2 Nanofibers andPVP (polyvinyl pyrrolidone) is 2-6: 1 in mass ratio, MXene nanosheets are dispersed in water, and then SiO is sequentially added 2 Homogenizing the nano-fibers and PVP for 20-40 minutes at 8000-12000 rpm by a homogenizer to obtain uniformly dispersed suspension; then magnetically stirring the dispersion liquid for 15-30 minutes and carrying out ultrasonic treatment for 30-60 minutes; treating the dispersion by directional freezing technology or random freezing technology, freeze-drying in a vacuum freeze-drying machine at a temperature below-50 deg.C and a pressure below 20Pa for more than 48h to obtain SiO 2 nanofiber/MXene aerogel.
4. A method according to claim 3, characterized in that the SiO produced is electrospun 2 The average diameter of the nanofibers was 300 nm; the thickness of the monolithic layer of MXene nanosheets was 1.59 nm.
5. The method as claimed in claim 3, wherein the directional freezing technique in step (3) is directional freezing using an ice template by vertically placing a copper column in a container containing liquid nitrogen, placing a square mold having the remaining portion insulated with heat only at the bottom end on the copper column, introducing the dispersion into the mold placed on the copper column, inducing directional growth of ice crystals from the bottom end to the top end by temperature difference between the bottom end of the mold and the top end of the mold, and ending the directional freezing process when the upper layer dispersion in the mold is completely frozen.
6. A method according to claim 3, characterized in that the SiO produced by directional freezing is 2 After the MX-1 aerogel is subjected to 50% compressive strain circulation for 100 times, the recovery rate is still high, the stress retention rate reaches 97.3%, and the maximum compressive strain can reach 90%; SiO frozen at will 2 After 100 cycles of 50% compressive strain,/MX-I, the stress retention remained only 72.1%.
7. The use of the silica nanofiber/MXene composite aerogel with dual barrier properties as claimed in claim 1 as a material with dual barrier properties of thermal insulation and high temperature/fire warning.
8. Use according to claim 7, wherein the thermal conductivity of the composite aerogel is as low as 21mW m at room temperature of 25 ℃ -1 K -1 Thermal conductivity of 25mW m lower than that of air -1 K -1 Has good heat insulation performance.
9. Use according to claim 7, SiO 2 The nanofiber/MXene composite aerogel can still keep a proper far-end temperature when placed in a high-temperature environment of 300 ℃ for 30min or in a cold environment of less than-30 ℃ for 30min, has good high-temperature heat insulation/low-temperature heat insulation performance and is used at the temperature of-30-300 ℃.
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