CoFe nanocapsule loaded magnetic carbon aerogel, and preparation method and application thereof

Abstract

The application discloses a kind of CoFe nanocapsule loaded magnetic carbon aerogel and its preparation method and application, belong to composite material technical field.Its preparation method includes: configuration contains cobalt acetate and trisodium citrate dihydrate aqueous solution, add equal volume TEMPO oxidation CNF aqueous solution, mix evenly and be named as A liquid;Configuration contains potassium ferricyanide aqueous solution, add equal volume TEMPO oxidation CNF aqueous solution, mix evenly and be named as B liquid;After A liquid, B liquid are mixed, 70~100 ℃ reaction, obtain the CNF aqueous solution of surface in-situ growth PBA;It is unidirectionally frozen, and PBA is obtained after freeze-drying CNF-based aerogel loaded;After heat treatment, it is obtained.The magnetic carbon aerogel has good mechanical flexibility, elasticity and fatigue resistance, excellent electrical conductivity and electromagnetic wave absorption performance, excellent electric / magnetic sensing performance, good heat insulation performance, and has broad application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite materials, and particularly relates to a CoFe nanocapsule loaded magnetic carbon aerogel and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of increasing the understanding of the background of the present application and does not necessarily pertain to the prior art that is already known in the field of the application.

[0003] The rapid development of Internet of Things technology puts forward higher requirements for high-performance multifunctional electronic devices, and multifunctional composite materials integrated with excellent mechanical flexibility, electromagnetic compatibility, thermal management capability and various sensing capabilities are highly favored. Compared with other carbon materials, polymer-derived porous carbon has inherent advantages such as adjustable electrical conductivity, flexible preparation, wide source, good processability and scalable production. By designing biomimetic cell morphology, such as ordered micropores, to construct a layered structure connected to each other, the mechanical strength and flexibility of carbon aerogel can be significantly enhanced. On this basis, magnetic substances, especially magnetic metals derived from metal-organic frameworks (MOFs), are loaded into porous carbon to prepare electromagnetically coupled composites, further expanding the application scenarios of the materials, such as electromagnetic sensing and electromagnetic compatibility.

[0004] Cellulose, which is stable, low-cost and environmentally friendly, can alleviate the pressure of excessive use of petrochemical raw materials and is considered an important component of future material industry. Cellulose nanofiber (CNF) has abundant functional groups (-OH, -COOH, etc.) on its surface, which enables CNF to have high compatibility and strong interaction with metal-organic frameworks (MOFs). At the same time, the metal ions in MOFs can be directly reduced to magnetic metals after carbonization, which can maintain the convenience of material preparation. Therefore, CNF / MOFs composite aerogel is an ideal choice for manufacturing various nanofunctional materials. However, the traditional bottom-up method for assembling nanocomposite aerogels has the problem of agglomeration of MOFs or MOFs derivatives at high loading, and the aggregation of nanoparticles inevitably leads to defect concentration and poor interface quality, resulting in failure of mechanical properties or other functions. The emerging method of growing MOFs in situ to preformed CNF-based aerogels can only attach MOF particles to the CNF wall, but cannot form sufficient surface contact, which is far from the aerogel with good dispersity and interface quality. Therefore, developing a simple and sustainable manufacturing strategy to achieve high uniform dispersion of MOF particles in CNF aerogel and high interface quality, so as to obtain high-performance, multifunctional magnetic carbon aerogel, is currently a very challenging task. SUMMARY

[0005] In order to solve the problems of the prior art, the present application aims to provide a CoFe nanocapsule-loaded magnetic carbon aerogel and a preparation method and application thereof, which has good mechanical flexibility, elasticity and fatigue resistance, while maintaining excellent electrical conductivity and electromagnetic wave absorption performance, excellent electric / magnetic sensing performance and good heat insulation performance, and has a wide application prospect.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] In a first aspect of the present application, a preparation method of a CoFe nanocapsule-loaded magnetic carbon aerogel is provided, comprising the following steps:

[0008] (1) An aqueous solution containing cobalt acetate and trisodium citrate dihydrate is configured, and an equal volume of an aqueous solution containing TEMPO-oxidized CNF is added, mixed and named as A liquid; an aqueous solution containing 2-20 g / L potassium ferricyanide is configured, and an equal volume of an aqueous solution containing TEMPO-oxidized CNF is added, mixed and named as B liquid;

[0009] (2) A liquid and B liquid are mixed at a volume ratio of 1:1-2, and then reacted in a water bath at 70-100 DEG C to obtain a CNF aqueous solution with PBA grown in situ on the surface;

[0010] (3) The CNF aqueous solution with PBA grown in situ on the surface is unidirectionally frozen, and then freeze-dried to obtain a PBA-loaded CNF-based aerogel; and the PBA-loaded CNF-based aerogel is heat-treated to obtain a CoFe nanocapsule-loaded magnetic carbon aerogel.

[0011] The present application utilizes in-situ growth technology to realize the high dispersion and close combination of PBA in cellulose aerogel, and a CoFe nanocapsule-loaded magnetic carbon aerogel can be obtained after high-temperature carbonization of the cellulose-based aerogel.

[0012] In some embodiments of the present application, in the aqueous solution containing cobalt acetate and trisodium citrate dihydrate, the concentration of cobalt acetate is 3-30 g / L, and the concentration of trisodium citrate dihydrate is 5-40 g / L.

[0013] In some embodiments of the present application, in the aqueous solution of TEMPO-oxidized CNF, the concentration of TEMPO-oxidized CNF is 0.7-2.0 wt%.

[0014] In some embodiments of the present application, in the aqueous solution containing potassium ferricyanide, the concentration of potassium ferricyanide is 4-50 g / L.

[0015] In some embodiments of the present application, in step (2), the reaction time is 8-24 hours.

[0016] In some embodiments of the present application, in step (2), after the reaction is completed, a blue-purple hydrogel is obtained, and after washing with deionized water to remove excess salt ions, the surface of the CNF aqueous solution of PBA is grown in situ after slight shaking.

[0017] In some embodiments of the present application, the unidirectional freezing comprises the following steps:

[0018] The CNF aqueous solution of PBA grown in situ on the surface is introduced into a mold with one metal side and the remaining sides being non-heat-conductive materials, and unidirectional freezing is performed under liquid nitrogen, and heat exchange is only performed on the metal side. The unidirectional freezing method enables the cellulose-based aerogel to have a porous honeycomb structure, which can be retained after carbonization.

[0019] In some embodiments of the present application, the conditions for freeze-drying are: temperature -60℃, and air pressure 3Pa.

[0020] In some embodiments of the present application, the conditions for heat treatment are: temperature 500-800℃, and time 1-4h.

[0021] In a second aspect of the present application, a CoFe nanocapsule-loaded magnetic carbon aerogel is provided, which is prepared by the above preparation method. The CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40mg / cm 3 , has a directional pore structure, and has a CoFe nanoparticle core with a diameter of 100-200nm and a carbon shell loaded on a carbon-based support wall.

[0022] By the above preparation method, a Prussian blue analog-loaded CNF-based aerogel can also be obtained, i.e., a CoFe nanocapsule-loaded magnetic carbon aerogel before carbonization, which has a density of 5-20mg / cm 3 , has a significant directional pore structure, and has a cubic PBA particle with a length of 200-400nm embedded in a CNF support wall.

[0023] In a third aspect of the present application, the above CoFe nanocapsule-loaded magnetic carbon aerogel is applied in the fields of electromagnetic wave absorbing materials, electric / magnetic sensing materials, micro-force sensing materials, thermal insulation materials, or wearable flexible electronics.

[0024] The present application has the following beneficial effects:

[0025] The CNF aqueous solution in which the Prussian blue analogues are grown in situ on the surface has excellent dispersion uniformity and stability, which is conducive to the realization of the high dispersion of PBA in aerogels and the close combination of PBA and cellulose after freeze-drying.

[0026] The cellulose-based aerogel obtained by the in-situ growth method has PBA cubic particles embedded in the cellulose skeleton, and the surface of the PBA cubic particles is covered with a layer of CNF, so that the PBA particles can be directly converted into nanocapsules coated with CoFe alloy after carbonization. This structural transformation cannot be achieved by the traditional mechanical mixing method or the method of pre-forming aerogels and then growing MOFs in situ.

[0027] The unidirectional freezing method makes the cellulose-based aerogel have a porous honeycomb structure, which can be retained after carbonization. This structure can effectively strengthen the mutual connection between carbon layers, avoid the inherent brittleness of carbon materials, and make the carbon aerogel have good flexibility, elasticity and fatigue resistance. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings accompanying the specification provided as part of this application use to provide further understanding of the application, and the illustrative embodiments of the application and explanations thereof serve to explain the application, and do not constitute an improper limitation on the application.

[0029] Figure 1 The actual photos of the CNF aqueous dispersion in which PBA is grown in situ on the surface, the PBA-loaded CNF-based aerogel and the CoFe nanocapsule-loaded magnetic carbon aerogel provided for Example 1;

[0030] Figure 2 The photos showing the flexibility and resilience and the compression stress-strain curve of the CoFe nanocapsule-loaded magnetic carbon aerogel provided for Example 3, wherein a is the photo of the sample before, during and after being pressed by a 200g weight, b is the stress-strain curve of the sample under 50% deformation and 1000 times compression, and c is the stress-strain curve of the sample under 90% deformation and 20 times compression;

[0031] Figure 3 The scanning electron micrograph of the PBA-loaded CNF-based aerogel provided for Example 1;

[0032] Figure 4 The scanning electron micrographs of the CoFe nanocapsule-loaded magnetic carbon aerogel provided for Example 1, Example 2 and Example 3, wherein a and b are the scanning electron micrographs of the sample provided for Example 1 at different magnifications, c and d are the scanning electron micrographs of the sample provided for Example 2 at different magnifications, and e and f are the scanning electron micrographs of the sample provided for Example 1 at different magnifications;

[0033] Figure 5 The electromagnetic parameter test results of the CoFe nanocapsule loaded magnetic carbon aerogel provided in Example 1, Example 2 and Example 3 are shown in the figures, wherein a is the complex permittivity of the sample provided in Example 1, b is the complex permeability of the sample provided in Example 1, c is the complex permittivity of the sample provided in Example 2, d is the complex permeability of the sample provided in Example 2, e is the complex permittivity of the sample provided in Example 3, and f is the complex permeability of the sample provided in Example 3;

[0034] Figure 6 The electromagnetic reflection loss results of the CoFe nanocapsule loaded magnetic carbon aerogel provided in Example 1, Example 2 and Example 3 are shown in the figures, wherein a is the electromagnetic reflection loss of the sample provided in Example 1, b is the electromagnetic reflection loss of the sample provided in Example 2, and c is the electromagnetic reflection loss of the sample provided in Example 3;

[0035] Figure 7 The electromagnetic wave absorption mechanism diagram of the CoFe nanocapsule loaded magnetic carbon aerogel provided in Example 2 is shown in the figure;

[0036] Figure 8 The magnetic response / sensing test results of the CoFe nanocapsule loaded magnetic carbon aerogel provided in Example 2 are shown in the figures;

[0037] Figure 9 The heat insulation test results of the CoFe nanocapsule loaded magnetic carbon aerogel provided in Example 4 are shown in the figures, wherein a is the upper surface temperature of the aerogel after being placed on a 100℃ metal heating plate for different time, b is the upper surface temperature of the aerogel after being placed on a metal heating plate at different temperatures for 10 minutes, and c is the infrared thermal imaging photo of the aerogel when placed on the palm. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0039] Glossary:

[0040] Interface quality: The interface quality refers to the interface bonding ability of the particles loaded at the aerogel skeleton. High interface quality leads to larger bonding area, greater bonding force, less damage to the skeleton structure, fewer defects, and stress concentration can be avoided.

[0041] One-way freezing: One-way freezing method is to wrap the mold containing the sample around and the bottom or top with a material with good heat insulation performance, only the remaining top or bottom pad with a metal sheet for heat exchange, and then freeze it.

[0042] As introduced in the background art, in view of the deficiencies in the prior art, the present application provides a preparation method of CoFe nanocapsule loaded magnetic carbon aerogel, CoFe nanocapsule loaded magnetic carbon aerogel prepared by the preparation method and application of the CoFe nanocapsule loaded magnetic carbon aerogel in various fields.

[0043] A preparation method of CoFe nanocapsule loaded magnetic carbon aerogel, comprising the following steps:

[0044] (1) Prepare an aqueous solution containing 3-30 g / L cobalt(II) acetate and 5-40 g / L trisodium citrate dihydrate, and add an equal volume of an aqueous solution containing 0.7-2.0 wt% 2,2,6,6-tetramethylpiperidine oxide (TEMPO) oxidized CNF, stir the mixture uniformly, and name it as A liquid;

[0045] (2) Prepare an aqueous solution containing 4-50 g / L potassium ferricyanide, and add an equal volume of an aqueous solution containing 0.7-2.0 wt% TEMPO oxidized CNF, stir the mixture uniformly, and name it as B liquid;

[0046] (3) Mix A liquid and B liquid according to a volume ratio of 1:1-2, then quickly transfer them to a covered container and react in a water bath at 70-100℃ for 8-24 hours to obtain a blue-violet hydrogel; wash the obtained blue-violet hydrogel with appropriate ionic water to remove excess salt ions, and obtain a CNF aqueous solution with PBA grown in situ on the surface after slight shaking;

[0047] (4) Pour the CNF aqueous solution with PBA grown in situ on the surface into a specially designed polytetrafluoroethylene mold with a copper bottom plate, and perform one-way freezing under the action of liquid nitrogen; then, freeze dry at a temperature of-60℃ and a gas pressure of 3 Pa until complete, and transfer the obtained PBA loaded CNF-based aerogel to a closed pressure-resistant steel reaction kettle, and heat treat at a temperature of 500-800℃ for 1-4 hours to obtain CoFe nanocapsule loaded magnetic carbon aerogel.

[0048] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific examples.

[0049] Example 1

[0050] A preparation method of CoFe nanocapsule loaded magnetic carbon aerogel, comprising the following steps:

[0051] (1) 0.075 g of cobalt (II) acetate and 0.125 g of trisodium citrate dihydrate were added to 20 mL of deionized water, continuously stirred until dissolved to obtain a uniform ionic liquid; 20 mL of an aqueous dispersion containing 1 wt% TEMPO-oxidized nanocellulose was prepared; the two liquids were mixed and stirred for a long time until uniform, and named as liquid A.

[0052] (2) 0.66 g of potassium ferricyanide was added to 30 mL of deionized water, continuously stirred until dissolved to obtain a uniform ionic liquid; 30 mL of an aqueous dispersion containing 1 wt% TEMPO-oxidized nanocellulose was prepared; the two liquids were mixed and stirred for a long time until uniform, and named as liquid B.

[0053] (3) After mixing liquids A and B in a volume ratio of 1:1, they were quickly transferred to a covered container and reacted in a water bath at 80°C for 12 hours to obtain a blue-purple hydrogel. The obtained blue-purple hydrogel was repeatedly washed with an appropriate amount of ionic water to remove excess salt ions, and after slight shaking, a CNF aqueous solution with PBA grown in situ on the surface was obtained.

[0054] (4) The CNF aqueous solution with PBA grown in situ on the surface was poured into a specially designed polytetrafluoroethylene mold with a copper bottom plate, and unidirectional freezing was performed under the action of liquid nitrogen. Subsequently, after freezing drying to completion under the conditions of a temperature of -60°C and a gas pressure of 3 Pa, the obtained PBA-loaded CNF-based aerogel was transferred to a closed pressure-resistant steel reaction kettle and heat-treated at a temperature of 650°C for 2 hours to obtain a CoFe nanocapsule-loaded magnetic carbon aerogel.

[0055] In this embodiment, a photograph of the CNF aqueous dispersion with PBA grown in situ on the surface during the material manufacturing process is shown in Figure 1 a, and a photograph of the PBA-loaded CNF-based aerogel is shown in Figure 1 b. The CNF aqueous dispersion with PBA grown in situ on the surface is a hydrogel dispersion with certain mechanical strength, indicating that there is a strong interaction between CNF and CNF and between CNF and PBA particles in the dispersion. The PBA-loaded CNF-based aerogel has a density of about 8.1 mg / cm 3 , and the finally obtained CoFe nanocapsule-loaded magnetic carbon aerogel has a density of about 18.6 mg / cm 3 , as shown in Figure 1 b and c, both aerogels can be easily supported on dandelion fluff.

[0056] As shown in Figure 3It can be seen that the PBA-loaded CNF-based aerogel material has a significant directional pore structure, with cubic PBA particles of approximately 45 μm width and approximately 400 nm edge length embedded in the CNF support wall. Figure 4 As can be seen from a and b, after high-temperature carbonization, the cubic PBA particles are transformed into a capsule structure, with CoFe nanoparticles at the core and a particle diameter of approximately 100-200 nm.

[0057] Depend on Figure 5 a and Figure 5 As can be seen from b, the magnetic carbon aerogel supported by the CoFe nanocapsules has a high complex permittivity and a low complex permeability, resulting in high loss capacity but relatively poor impedance matching. Figure 6 As can be seen from a, the magnetic carbon aerogel can achieve effective absorption in the 6.4-18.0 GHz range with a matching thickness of 1-5 mm, and achieves a minimum reflection loss of -62.5 dB at 17.9 GHz with a matching thickness of 1.4 mm. At a matching thickness of 1.8 mm, the magnetic carbon aerogel achieves its maximum effective absorption bandwidth of 4.7 GHz.

[0058] Example 2

[0059] A method for preparing a magnetic carbon aerogel supported on CoFe nanocapsules includes the following steps:

[0060] (1) Add 0.15g cobalt(II) acetate and 0.25g trisodium citrate dihydrate to 20mL of deionized water and stir continuously until dissolved to obtain a uniform ionic liquid; prepare 20mL of aqueous dispersion containing 1wt% TEMPO oxidized nanocellulose; mix the two liquids and stir for a long time until uniform, and name it solution A.

[0061] (2) Add 0.132g potassium ferricyanide to 30mL of deionized water and stir continuously until dissolved to obtain a uniform ionic liquid; prepare 30mL of aqueous dispersion containing 1wt% TEMPO oxidized nanocellulose; mix the two liquids and stir for a long time until uniform, and name it solution B.

[0062] (3) Mix solution A and solution B at a volume ratio of 1:1, quickly transfer to a covered container and react in a water bath at 80°C for 12 hours to obtain a blue-purple hydrogel. Rinse the obtained blue-purple hydrogel repeatedly with an appropriate amount of deionized water to remove excess salt ions, and after slight shaking, obtain a CNF aqueous solution for in-situ growth of PBA on the surface.

[0063] (4) The CNF aqueous solution with PBA grown in situ on the surface was poured into a specially designed polytetrafluoroethylene mold with a copper base plate, and unidirectional freezing was performed under the action of liquid nitrogen. Subsequently, after freeze-drying to completion at a temperature of -60°C and an air pressure of 3 Pa, the obtained PBA-loaded CNF-based aerogel was transferred to a closed pressure-resistant steel reaction kettle, and heat-treated at a temperature of 650°C for 2 hours to obtain CoFe nanocapsule-loaded magnetic carbon aerogel.

[0064] In this embodiment, the density of the PBA-loaded CNF-based aerogel is about 10.6 mg / cm 3 , and the density of the finally obtained CoFe nanocapsule-loaded magnetic carbon aerogel is about 22.4 mg / cm 3 .

[0065] From Figure 4 c and d, it can be seen that after high-temperature carbonization, the cubic PBA particles are converted into a capsule structure, with CoFe nanoparticles as the core and a particle diameter of about 100-200 nm. Compared with Example 1, the loading density of CoFe nanocapsules on the carbon skeleton is higher.

[0066] From Figure 5 c and Figure 5 d, it can be seen that the CoFe nanocapsule-loaded magnetic carbon aerogel has moderate complex permittivity and moderate complex permeability, and the material has good loss capacity and impedance matching capacity. From Figure 6 b, it can be seen that the magnetic carbon aerogel can achieve effective absorption in the range of 4.3-18.0 GHz under a matching thickness of 1-5 mm, and exhibits two strong absorption peaks, i.e., a reflection loss of -70.8 dB achieved at 2.4 mm and 12.8 GHz, and a reflection loss of -64.0 dB achieved at 2.0 mm and 15.5 GHz. When the matching thickness is 2.3 mm, the magnetic carbon aerogel achieves a maximum effective absorption bandwidth of 6.0 GHz, which can completely cover the electromagnetic waves in the X-band.

[0067] Through analysis of the electromagnetic wave absorption mechanism of the CoFe nanocapsule-loaded magnetic carbon aerogel, it is found that the high dispersibility and biomimetic ordered porous morphology of CoFe nanocapsules in the carbon sheets optimize the impedance matching conditions, making it easier for electromagnetic waves to enter the aerogel. The constructed layered microstructure induces multiple reflections of electromagnetic waves, prolongs the electromagnetic wave transmission path, and promotes the dissipation capacity of the material. In addition to the good electrical conductivity and magnetic loss capacity of the carbon wall of the carbon aerogel, the dispersibility of the magnetic particles and the improvement of the interface quality significantly enhance the interface polarization relaxation capacity of the material, making the electromagnetic attenuation path more sufficient and diversified.

[0068] Due to the small elastic modulus (2.96 kPa), high elasticity and good electrical conductivity of the CoFe nanocapsule-loaded magnetic carbon aerogel, the aerogel has the ability of micro-force sensing, and has potential application prospects in precision instruments or wearable devices. In particular, the introduction of magnetic metal enables the carbon aerogel to additionally obtain unique magnetic sensing capability. It is found through magnetic sensing test that when a magnetic field is loaded at one end of the cuboid aerogel, the aerogel produces obvious bending deformation. In the bending process, one side of the aerogel is compressed to shorten the electron transport path, so that the resistance is reduced, and thus the resistance value can be used to judge the strength of the magnetic field in which the aerogel is located. As shown in FIG. 8, when a magnetic field with a strength of 260 mT is loaded at one end of the magnetic carbon aerogel, the bending angle of the aerogel can exceed 28°, and at the same time, about 10% resistance change can be detected, indicating that it has extremely high sensitivity; and when in a periodically loaded magnetic field, repeatable resistance change can be detected, indicating that the magnetic carbon aerogel has extremely high reliability for magnetic sensing. Figure 8

[0069] Example 3

[0070] A preparation method of a CoFe nanocapsule-loaded magnetic carbon aerogel comprises the following steps:

[0071] (1) 0.3 g of cobalt (II) acetate and 0.5 g of trisodium citrate dihydrate are added to 20 mL of deionized water, and stirring is continued until dissolution to obtain a uniform ionic liquid; a 20 mL aqueous dispersion containing 1 wt% TEMPO oxidized nanocellulose is prepared; the two liquids are mixed and stirred for a long time until uniform, and are named as A liquid.

[0072] (2) 0.264 g of potassium ferricyanide is added to 30 mL of deionized water, and stirring is continued until dissolution to obtain a uniform ionic liquid; a 30 mL aqueous dispersion containing 1 wt% TEMPO oxidized nanocellulose is prepared; the two liquids are mixed and stirred for a long time until uniform, and are named as B liquid.

[0073] (3) A liquid and B liquid are mixed according to a volume ratio of 1:1, then are quickly transferred to a covered container and reacted in a water bath at 80℃ for 12 hours to obtain a blue-violet hydrogel. The obtained blue-violet hydrogel is repeatedly washed with appropriate ionic water to remove excess salt ions, and after slight shaking, a CNF aqueous solution with PBA grown in situ on the surface is obtained.

[0074] ​(4) The CNF aqueous solution with PBA grown on the surface in situ was poured into a specially designed PTFE mold with a copper base plate, and unidirectional freezing was performed under the action of liquid nitrogen. Subsequently, after freeze-drying to completion at a temperature of -60°C and an air pressure of 3 Pa, the obtained PBA-loaded CNF-based aerogel was transferred to a closed pressure-resistant steel reaction kettle, and heat treatment was performed at a temperature of 650°C for 2 hours to obtain CoFe nanocapsule-loaded magnetic carbon aerogel.

[0075] In this embodiment, the density of the PBA-loaded CNF-based aerogel is about 17.7 mg / cm 3 , and the density of the finally obtained CoFe nanocapsule-loaded magnetic carbon aerogel is about 27.3 mg / cm 3 .

[0076] From Figure 4 e and Figure 4 f, it can be seen that after high-temperature carbonization, the cubic PBA particles are converted into a capsule structure, the core is a CoFe nanoparticle, the particle diameter is about 100-200 nm, and compared with Embodiments 1 and 2, the loading density of the CoFe nanocapsule on the carbon skeleton is further increased.

[0077] From Figure 5 e and Figure 5 f, it can be seen that the CoFe nanocapsule-loaded magnetic carbon aerogel has a lower complex permittivity and a higher complex permeability, and the impedance matching characteristics of the material are further optimized. However, since the magnetic carbon aerogel is a wave-absorbing material dominated by electrical loss, the decrease in the complex permittivity leads to a decrease in the loss capacity of the material. From Figure 6 c, it can be seen that under a matching thickness of 1-5 mm, the magnetic carbon aerogel can only achieve a minimum reflection loss of -14.7 dB at 5.0 mm and 6.3 GHz, and the maximum effective absorption bandwidth is only 2.4 GHz at 3.3 mm. Compared with Embodiments 1 and 2, the wave-absorbing capacity of the magnetic carbon aerogel in this embodiment has decreased.

[0078] For polymer-derived carbon materials, it is often difficult to obtain good mechanical elasticity. However, in this embodiment, as shown in Figure 2 a, even under a very high magnetic particle loading (44%), the carbon aerogel still has excellent compressibility, flexibility, elasticity and fatigue resistance, which is due to the interconnected layered porous microstructure of the magnetic carbon aerogel and the excellent interface quality between the particles and the carbon wall. The obtained compression stress-strain curve after 1000 compression cycles with a deformation of 50% is as shown in Figure 2b. The magnetic carbon aerogel can maintain more than 80.2% of the maximum stress and the permanent deformation is less than 3.3% after 1000 compressions, which indicates that the aerogel can withstand a large elastic deformation without obvious structural collapse. As shown in Figure 2 c. Even under the compression condition of a large deformation of 90%, the aerogel can still recover 77.9% of the initial height and maintain 42.8% of the maximum stress after 20 compression-release cycles. These results show that the magnetic carbon aerogel has excellent mechanical properties.

[0079] Example 4

[0080] A method for preparing a CoFe nanocapsule-loaded magnetic carbon aerogel comprises the following steps:

[0081] (1) 0.15 g of cobalt (II) acetate and 0.25 g of trisodium citrate dihydrate were added to 20 mL of deionized water, and stirring was continued until dissolution to obtain a uniform ionic liquid; a 20 mL aqueous dispersion containing 1 wt% TEMPO-oxidized nanocellulose was prepared; the two liquids were mixed and stirred for a long time until uniform, and were named as liquid A.

[0082] (2) 0.132 g of potassium ferricyanide was added to 30 mL of deionized water, and stirring was continued until dissolution to obtain a uniform ionic liquid; a 30 mL aqueous dispersion containing 1 wt% TEMPO-oxidized nanocellulose was prepared; the two liquids were mixed and stirred for a long time until uniform, and were named as liquid B.

[0083] (3) After mixing liquid A and liquid B at a volume ratio of 1:1, they were quickly transferred to a covered container and reacted in a water bath at 80°C for 24 hours to obtain a blue-violet hydrogel. The obtained blue-violet hydrogel was repeatedly washed with appropriate ionic water to remove excess salt ions, and after slight shaking, a CNF aqueous solution with PBA grown in situ on the surface was obtained.

[0084] (4) The CNF aqueous solution with PBA grown in situ on the surface was poured into a specially designed polytetrafluoroethylene mold with a copper bottom plate, and unidirectional freezing was performed under the action of liquid nitrogen. Subsequently, after freeze-drying to completion at a temperature of -60°C and a gas pressure of 3 Pa, the obtained PBA-loaded CNF-based aerogel was transferred to a closed pressure-resistant steel reaction kettle and heat-treated at a temperature of 650°C for 2 hours to obtain a CoFe nanocapsule-loaded magnetic carbon aerogel.

[0085] The macroscopic and microscopic structures of the magnetic carbon aerogel obtained in this example are highly similar to those of the above examples, and the CoFe nanocapsule-loaded carbon aerogel with a directional porous structure is also obtained.

[0086] The magnetic carbon aerogel was cut into cuboids with a thickness of 1.2 mm, placed on a metal heating plate at 100°C, and the temperature of the upper surface of the aerogel was measured at different times. Figure 9 As shown in Figure a, after continuous heating for 1 minute, 5 minutes, and 10 minutes, the surface temperature of the aerogel remained at approximately 35.9°C, 36.3°C, and 37.7°C, respectively. Even after continuous heating for 30 minutes, the surface temperature remained at 39.2°C. Similarly, the carbon aerogel cuboid was placed on a heating plate and heated at different temperatures for 10 minutes. Figure 9 As shown in b, after heating the aerogel at 80℃, 100℃, 120℃, 140℃, and 160℃ for 10 minutes, the surface temperature remained at 33.6℃, ​​36.2℃, 39.1℃, 43.2℃, and 51.4℃, respectively. These results indicate that the magnetic carbon aerogel possesses low thermal conductivity and excellent thermal insulation capabilities. Furthermore, placing the aerogel cube in the palm of a human hand and detecting it using infrared thermal imaging, as shown... Figure 9 As shown in c, the surface temperature of the aerogel is very close to the ambient temperature, indicating that the carbon aerogel has great application potential in infrared stealth, wearable devices and other fields.

[0087] Example 5

[0088] A method for preparing a magnetic carbon aerogel supported on CoFe nanocapsules includes the following steps:

[0089] (1) Add 0.15g cobalt(II) acetate and 0.25g trisodium citrate dihydrate to 20mL of deionized water and stir continuously until dissolved to obtain a uniform ionic liquid; prepare 20mL of aqueous dispersion containing 1wt% TEMPO oxidized nanocellulose; mix the two liquids and stir for a long time until uniform, and name it solution A.

[0090] (2) Add 0.132g potassium ferricyanide to 30mL of deionized water and stir continuously until dissolved to obtain a uniform ionic liquid; prepare 30mL of aqueous dispersion containing 1wt% TEMPO oxidized nanocellulose; mix the two liquids and stir for a long time until uniform, and name it solution B.

[0091] (3) Mix solution A and solution B at a volume ratio of 1:1, quickly transfer to a covered container and react in a water bath at 80°C for 12 hours to obtain a blue-purple hydrogel. Rinse the obtained blue-purple hydrogel repeatedly with an appropriate amount of deionized water to remove excess salt ions, and after slight shaking, obtain a CNF aqueous solution for in-situ growth of PBA on the surface.

[0092] (4) The CNF aqueous solution with PBA grown in situ on the surface is poured into a specially designed polytetrafluoroethylene mold with a copper bottom plate, and unidirectional freezing is performed under the action of liquid nitrogen. Subsequently, after freeze-drying to completion at a temperature of-60℃ and an air pressure of 3 Pa, the obtained PBA-loaded CNF-based aerogel is transferred to a closed pressure-resistant steel reaction kettle, and heat-treated at a temperature of 750℃ for 2 hours to obtain CoFe nanocapsule-loaded magnetic carbon aerogel.

[0093] The macroscopic and microscopic structures of the magnetic carbon aerogel obtained in this example are highly similar to those of the above examples, and the CoFe nanocapsule-loaded carbon aerogel with CoFe as the core also has potential applications in electromagnetic wave absorption, pressure / magnetic sensing, and thermal insulation, etc.

[0094] Comparative Example 1

[0095] A Co3Fe7 / CNF carbon aerogel is prepared according to the method “2.3 Experimental Methods” in “Zhang Z, Liu B, Fang Y, et al. Preparation of bacterial cellulose Co3Fe7 / CNF aerogel with high wave-absorbing performance[J]. China Material Progress, 2022, 41(7): 563-572. DOI:10.7502 / j.issn.1674-3962.202008020.” as follows:

[0096] “2.3.1 Purification of bacterial cellulose

[0097] Large-size bacterial cellulose sheets ( Figure 1 b) are cut into small pieces of 4 cm x 3 cm, and the bacterial cellulose small pieces are mixed with a 2% (mass fraction, the same below) NaOH solution at a volume ratio of 1:3, heated to 100℃ and stirred for 24 h, and then the alkali-washed bacterial cellulose small pieces are taken out and washed with pure water for 3 times; then they are mixed with a 1.5% CH3COOH solution at a volume ratio of 1:3, heated to 100℃ and stirred for 24 h, and finally the acid- and alkali-treated bacterial cellulose is repeatedly ultrasonically cleaned with distilled water until pH=7.

[0098] 2.3.2 Preparation of Co3Fe7 / CNF aerogel

[0099] Figure 1 a is the preparation process of Co3Fe7 / CNF aerogel, and the purified bacterial cellulose small pieces are immersed in a mixed solution of 0.01 mol / L Co(NO3)2 and 0.02 mol / L Fe(NO3)3 for 48 h, so that the bacterial cellulose small pieces fully adsorb Co 2+ and Fe 3+The bacterial cellulose small pieces loaded with cobalt-iron ions were immersed in liquid nitrogen (-196℃) for 20 min to freeze them thoroughly, and then freeze-dried (-74℃, 1 Pa) for 72 h. This sample was labeled as Co 2+ Fe 3+ / BC aerogel; finally, the temperature was raised to the carbonization temperature at a rate of 5℃ / min under nitrogen atmosphere in a tube furnace and kept for 2 h. After carbonization, the furnace was cooled to room temperature. The carbonization temperature gradient was set to 600, 700, 800 and 900℃, respectively. The Co3Fe7 / CNF aerogels obtained at different carbonization temperatures were labeled as Co3Fe7 / CNF-600, Co3Fe7 / CNF-700, Co3Fe7 / CNF-800 and Co3Fe7 / CNF-900, respectively. Figure 1 c are photos of the bacterial cellulose aerogel at different processing stages.

[0100] Compared with the existing magnetic particle loaded cellulose carbon aerogel, such as the Co3Fe7 / CNF carbon aerogel of Comparative Example 1, the CoFe nanocapsule loaded magnetic carbon aerogel described in the present application has a unique microstructure, higher electromagnetic reflection loss, better mechanical properties, and expanded heat insulation performance, sensing performance, etc.

[0101] Firstly, the Comparative Example 1 uses the traditional impregnation method to first obtain a metal salt loaded cellulose-based aerogel, which is carbonized at high temperature to obtain a microstructure of CoFe magnetic particles loaded on the surface of the carbon skeleton. The magnetic particles in this structure will directly cause the surrounding carbon skeleton to have more defects and stress concentration, resulting in the decline of various properties, especially the mechanical properties. The CoFe nanocapsule loaded magnetic carbon aerogel described in the present application first grows PBA particles in situ in the precursor solution, making PBA tightly combined with CNF. After freeze-drying, an aerogel is obtained in which PBA is embedded in the cellulose-based skeleton. After high-temperature carbonization, PBA is converted into a capsule structure with CoFe particles as the core and carbon as the shell, which is tightly combined with the carbonized CNF skeleton. This structure has not been obtained in any related research. This special microstructure avoids the generation of defects and stress concentration, and can significantly improve the mechanical properties and wave absorption performance of the material.

[0102] Secondly, compared with the Co3Fe7 / CNF carbon aerogel in Comparative Example 1, which obtains a minimum reflection loss of -47.5 dB and an effective absorption bandwidth of 4.5-18 GHz, the CoFe nanocapsule loaded magnetic carbon aerogel described in Example 2 of the present application obtains a reflection loss of -70.8 dB and an effective absorption bandwidth of 4.3-18 GHz, and the effective absorption bandwidth frequency band at a single thickness covers all X bands, which completely exceeds the wave absorption performance of the Co3Fe7 / CNF carbon aerogel in Comparative Example 1.

[0103] Again, due to the directional pore structure, unique capsule loading structure and better interface quality of the CoFe nanocapsule-loaded magnetic carbon aerogel in the present application, it has mechanical flexibility, elasticity and fatigue resistance that the Co3Fe7 / CNF carbon aerogel in Comparative Example 1 does not have. For example, the magnetic particle loading of the magnetic carbon aerogel described in Example 3 is as high as 44%, but after 1000 compression cycles with a deformation of 50%, it can still maintain a maximum stress of more than 80.2% and a residual strain of less than 3.3%. Even under the condition of a compression of 90% deformation, after 20 compression and release cycles, the magnetic carbon aerogel can still recover 77.9% of the initial height and maintain a maximum stress of 42.8%. The mechanical flexibility, elasticity and fatigue resistance of the magnetic carbon aerogel endow it with unique applications in pressure sensing, magnetic sensing and the like.

[0104] Finally, the CoFe nanocapsule-loaded magnetic carbon aerogel in the present application also has good heat insulation capacity that the Co3Fe7 / CNF carbon aerogel in Comparative Example 1 does not have, which is due to the extremely low density and directional pore design of the CoFe nanocapsule-loaded magnetic carbon aerogel in the present application. For example, the magnetic carbon aerogel cube described in Example 4 can still maintain an upper surface temperature of 39.2°C after heating on a heating plate at 100°C for 30 minutes; even after heating on a heating plate at 160°C for 10 minutes, it can still maintain an upper surface temperature of 51.4°C, indicating that the CoFe nanocapsule-loaded magnetic carbon aerogel in the present application has good heat insulation capacity.

[0105] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing CoFe nanocapsule loaded magnetic carbon aerogel, characterized in that, It comprises the following steps: (1) preparing an aqueous solution containing cobalt acetate and trisodium citrate dihydrate, and adding an equal volume of an aqueous solution containing TEMPO-oxidized cellulose nanofiber, mixing and naming as A liquid; preparing an aqueous solution containing potassium ferricyanide, and adding an equal volume of an aqueous solution containing TEMPO-oxidized cellulose nanofiber, mixing and naming as B liquid; (2) mixing A liquid and B liquid at a volume ratio of 1:1-2, and then reacting at 70-100℃ to obtain an aqueous solution of cellulose nanofiber with Prussian blue analogues grown in situ on the surface; (3) unidirectionally freezing the aqueous solution of cellulose nanofiber with Prussian blue analogues grown in situ on the surface, and then freeze-drying to obtain cellulose nanofiber-based aerogel loaded with Prussian blue analogues; after heat treatment of the cellulose nanofiber-based aerogel loaded with Prussian blue analogues, CoFe nanocapsule-loaded magnetic carbon aerogel is obtained; The heat treatment is carried out in a closed pressure-resistant steel reactor; the heat treatment conditions are: temperature 500-800℃, time 1-4 h.

2. The production method according to claim 1, wherein In the aqueous solution containing cobalt acetate and trisodium citrate dihydrate, the concentration of cobalt acetate is 3-30 g / L, and the concentration of trisodium citrate dihydrate is 5-40 g / L.

3. The production method according to claim 1, wherein In the aqueous solution of TEMPO-oxidized cellulose nanofiber, the concentration of TEMPO-oxidized cellulose nanofiber is 0.7-2.0 wt%.

4. The production method according to claim 1, wherein In the aqueous solution containing potassium ferricyanide, the concentration of potassium ferricyanide is 4-50 g / L.

5. The production method according to claim 1, wherein In step (2), the reaction time is 8-24 hours.

6. The production method according to claim 1, wherein After the reaction in step (2) is completed, a blue-purple hydrogel is obtained, which is washed with deionized water to remove excess salt ions, and then subjected to slight oscillation to obtain an aqueous solution of cellulose nanofiber with Prussian blue analogues grown in situ on the surface.

7. The production method according to claim 1, wherein The unidirectional freezing comprises the following steps: The aqueous solution of cellulose nanofiber with Prussian blue analogues grown in situ on the surface is introduced into a mold with one metal side and the other non-heat-conducting material sides, and unidirectional freezing is carried out under liquid nitrogen, and only the metal side exchanges heat.

8. The production method according to claim 1, wherein The freeze-drying conditions are: temperature -60℃, and air pressure 3 Pa.

9. A CoFe nanocapsule loaded magnetic carbon aerogel, characterized in that, The CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aerogel has a density of 10-40 mg / cm 3 , and the CoFe nanocapsule-loaded magnetic carbon aer 10. The use of the CoFe nanocapsule-loaded magnetic carbon aerogel of claim 9 in electromagnetic wave absorbing materials, electric / magnetic sensing materials, micro-force sensing materials, and thermal insulation materials.

11. The use of the CoFe nanocapsule-loaded magnetic carbon aerogel of claim 9 in the field of wearable flexible electronics.

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