Conductive MOF (Metal Organic Framework) wave-absorbing aerogel with fractal microstructure as well as preparation method and application of conductive MOF wave-absorbing aerogel

Abstract

The invention discloses conductive MOF (Metal Organic Framework) wave-absorbing aerogel with a fractal microstructure as well as a preparation method and application of the conductive MOF wave-absorbing aerogel, and belongs to the technical field of aerogel preparation. The preparation method provided by the invention comprises the following steps: carrying out deacetylation treatment on cellulose acetate fibers containing blocked isocyanate, and then preparing a fiber suspension; adding hexaaminotriphenylene hexahydrochloride and nickel salt into the fiber suspension, mixing and dissolving, adding alkali liquor, heating to 50-90 DEG C, stirring for a set time, and reacting in a sealed manner to obtain composite fibers; and dispersing the composite fiber in water, and sequentially performing freeze-shaping, freeze-drying and thermal crosslinking to obtain the composite fiber. The obtained conductive MOF wave-absorbing aerogel shows excellent electromagnetic wave absorption performance, the reflection loss can reach-61 dB at the frequency of 13.84 GHz, the optimal effective absorption bandwidth reaches 8 GHz or above, and the conductive MOF wave-absorbing aerogel has the characteristics of light weight and broadband absorption and has good application prospects in the field of electromagnetic wave absorption.

Description

Technical Field

[0001] This invention relates to the field of aerogel preparation technology, and in particular to a conductive MOF absorbing aerogel with fractal microstructure, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Metal-organic frameworks (MOFs) are crystalline porous materials with a periodic network structure, formed by coordination bonds between metal ions or metal clusters and organic ligands. As an important branch of MOF materials, conductive MOFs are constructed through the coordination interaction between metal ions and π-conjugated organic ligands. Their outstanding characteristics include high crystallinity, large specific surface area, tunable pore size, uniform channels, dense active sites, and intrinsically high conductivity, effectively overcoming the technical bottleneck of insufficient conductivity in traditional MOF materials. With these advantages, conductive MOFs show broad application prospects in supercapacitors, chemical sensing, catalysis, batteries, and seawater desalination. Especially in the field of electromagnetic wave absorbing materials, their inherent porous structure, abundant active sites, and tunable microstructure make them an ideal candidate system for developing "thin, lightweight, wide, and strong" high-performance electromagnetic wave absorbing materials.

[0004] Aerogels are a class of nanoscale porous solid materials prepared by the sol-gel method combined with specific drying processes. Their most significant characteristics are extremely high porosity and specific surface area, leading to their wide application in adsorption, catalysis, thermal management, and electromagnetic wave absorption. In the field of microwave absorption, the unique structure of aerogels can enhance performance through a dual mechanism: firstly, by enhancing impedance matching to broaden the electromagnetic wave absorption bandwidth; and secondly, by promoting electromagnetic wave loss efficiency through multiple reflection effects.

[0005] Preparing conductive MOFs into aerogel materials not only retains their inherent lightweight and porous properties but also overcomes the application limitations of conductive MOFs existing only in powder form, providing a better technical path for promoting their practical application. However, current research faces multiple challenges: First, the weak interparticle bonding and loose intrinsic structure of conductive MOFs severely restrict the construction of three-dimensional self-supporting aerogels; second, the high contact resistance between conductive MOF particles and the high porosity of the aerogel result in insufficient dielectric loss, which needs to be compensated for by increasing the filling amount. However, high filling amounts lead to increased costs and density, thus limiting their practical applications. Currently, the structure-function integration research of conductive MOFs is still mainly focused on thin film systems, and progress in the field of three-dimensional self-supporting aerogels is slow. The core bottleneck lies in how to construct efficient electron transport channels between conductive MOFs within the macroscopic aerogel framework. This key issue directly determines the realization of the material's electromagnetic absorption potential and multifunctional synergistic effects. Summary of the Invention

[0006] In view of this, the present invention provides a conductive MOF absorbing aerogel with fractal microstructure, its preparation method and application. The conductive MOF absorbing aerogel provided by the present invention improves the electron transport efficiency of the conductive MOF in the aerogel through special structural design, thereby solving the problems of insufficient conductivity loss and poor absorption performance under three-dimensional self-supporting structure.

[0007] In a first aspect, the present invention provides a method for preparing a conductive MOF absorbing aerogel with a fractal microstructure, comprising the following steps: Cellulose acetate fibers containing blocked isocyanates are deacetylated and then made into fiber suspensions. Hexaaminotriphenyl hexahydrochloride and nickel salt were added to the fiber suspension, mixed and dissolved, and then an alkaline solution was added. The temperature was then raised to 50-90°C and stirred for a set time before being sealed for reaction to obtain composite fiber. The composite fibers are dispersed in water and then subjected to freeze-setting, freeze-drying and thermal cross-linking in sequence to obtain the final product.

[0008] Preferably, the cellulose acetate fiber is selected from one or more of cellulose acetate fiber, cellulose diacetate fiber, or cellulose triacetate fiber; the nickel salt is selected from one or more of nickel chloride, nickel nitrate, or nickel sulfate.

[0009] Preferably, the deacetylation treatment step is as follows: homogenizing cellulose acetate fibers containing blocked isocyanate and then placing them in an alkaline solution, reacting at 20~40℃ for 4~12h.

[0010] Furthermore, the alkaline solution is one or more of NaOH, KOH, or Ba(OH)2 aqueous solution, and the concentration of the alkaline solution is 5~30 g / L.

[0011] Preferably, the concentration of the fiber suspension is 2-10 g / L, and the solvent is water; the ratio of the fiber suspension to hexaaminotriphenyl hexahydrochloride is 10 mL : (15-120) mg; and the molar ratio of hexaaminotriphenyl hexahydrochloride to nickel salt is 2 : (2-4).

[0012] Preferably, in the step of adding alkaline solution after mixing and dissolving, the volume ratio of alkaline solution to fiber suspension is 1:(4~8); the alkaline solution is ammonia water with a mass fraction of 23~30wt%.

[0013] Preferably, in the step of heating to 50~90℃ and stirring for a set time, the stirring time is 0.5~3h; and the sealed reaction time is 2~6h.

[0014] Preferably, in the step of dispersing the composite fiber in water, the concentration of the composite fiber is 30~50 mg / mL; the temperature of the thermal crosslinking is 100~140℃, and the time is 1~6 h.

[0015] Secondly, the present invention provides a conductive MOF absorbing aerogel with fractal microstructure prepared by the above preparation method.

[0016] Thirdly, the present invention provides the application of the above-mentioned conductive MOF absorbing aerogel with fractal microstructure in the field of electromagnetic wave absorption.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention achieves simultaneous control of in-situ growth and fiber etching of conductive MOFs by deacetylation of cellulose acetate fibers containing blocked isocyanates, followed by synergistic action with hexaaminotriphenylene hexahydrochloride, nickel salt, and alkaline solution. In this preparation method, the alkaline solution acts as a deprotonating agent to neutralize the ligand hydrochloric acid to promote MOF nucleation and growth, and also partially etches the fibers, endowing them with fractal microstructures and a larger specific surface area, thereby providing abundant active sites and heterogeneous interfaces for the MOFs; at the same time, the preparation method of this invention is simple and easy to achieve large-scale production.

[0018] (2) This invention constructs an aerogel structure through fiber composite and thermal crosslinking process, which breaks through the limitations of traditional conductive MOF powder materials in molding and application, and effectively solves the problem of insufficient electrical conductivity loss caused by excessive contact resistance of conductive MOF aerogel, thus realizing the synergistic improvement of the structural stability and electromagnetic loss capability of the microwave absorbing material.

[0019] (3) The conductive MOF absorbing aerogel prepared by the present invention exhibits excellent electromagnetic wave absorption performance. Its reflection loss can reach -61 dB at a frequency of 13.84 GHz, and its optimal effective absorption bandwidth is above 8 GHz. It has both lightweight and wideband absorption characteristics and has good application prospects in the field of electromagnetic wave absorption. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 These are transmission electron microscope images of the deacetylated fibers in Example 1 of this invention; Figure 2 These are transmission electron microscope images of conductive MOF aerogels with fractal microstructures in Embodiment 1 of the present invention; Figure 3 These are scanning electron microscope images of the conductive MOF aerogel with fractal microstructure in Embodiment 1 of the present invention; Figure 4 This is a transmission electron microscope image of the deacetylated fiber after etching with ammonia water in Example 1 of the present invention; Figure 5 These are scanning electron microscope images of the simple mixed conductive MOF aerogel prepared in Comparative Example 1 of this invention. Figure 6 The BET micropore size distribution (A) and mercury porosimetry macropore size distribution (B) are of the conductive MOF aerogel with fractal microstructure in Example 1 of the present invention and the simple mixed conductive MOF aerogel in Comparative Example 1. Figure 7 The images show the XRD patterns of the pure MOF material (Ni-HITP) obtained by reacting cellulose acetate fiber, hexaaminotriphenyl hexahydrochloride and nickel nitrate hexahydrate, the conductive MOF aerogel with fractal microstructure of Example 1, and the simple mixed conductive MOF aerogel of Comparative Example 1. Figure 8 These are macroscopic photographs of the conductive MOF aerogel with fractal microstructure prepared in Example 1 of this invention under 1000 times pressure and when placed on foxtail grass. Figure 9 These are images of the conductive MOF aerogel with fractal microstructure prepared in Example 1 of this invention, after being immersed in water and dried. Figure 10The dielectric constant diagrams are of the conductive MOF absorbing aerogel with fractal microstructure in Embodiment 1 of the present invention and the conductive MOF absorbing aerogel in Comparative Example 1. Figure 11 The diagram shows the reflection loss performance of the conductive MOF absorbing aerogel with fractal microstructure in Example 1 of the present invention and the conductive MOF absorbing aerogel in Comparative Example 1. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, 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 invention pertains.

[0023] This invention provides a method for preparing a conductive MOF absorbing aerogel with a fractal microstructure, comprising the following steps: Cellulose acetate fibers containing blocked isocyanates are deacetylated and then made into fiber suspensions. Hexaaminotriphenyl hexahydrochloride and nickel salt were added to the fiber suspension, mixed and dissolved, and then an alkaline solution was added. The temperature was then raised to 50-90°C and stirred for a set time before being sealed for reaction to obtain composite fiber. The composite fibers are dispersed in water and then subjected to freeze-setting, freeze-drying and thermal cross-linking in sequence to obtain the final product.

[0024] The above-mentioned technical solution of the present invention achieves the construction of conductive MOF absorbing aerogel with fractal microstructure through multi-step synergistic action. First, after deacetylation treatment of cellulose acetate fibers containing blocked isocyanate, the acetyl groups on the fiber surface are partially removed, exposing more hydroxyl active sites; the prepared fiber suspension ensures uniform fiber distribution through dispersion, providing three-dimensional scaffold support for subsequent MOF growth.

[0025] After adding hexaaminotriphenylene hexahydrochloride (CAS No.: 1350518-27-2) and nickel salt to the fiber suspension, the alkaline solution in the system first neutralizes the hydrochloric acid in the hexaaminotriphenylene hexahydrochloride ligand, releasing the free amino ligand, which then undergoes a coordination reaction with nickel ions under a warm condition of 50~90℃, realizing the in-situ nucleation and growth of conductive MOF on the fiber surface and in the pores. At the same time, the alkaline environment etches the cellulose acetate fibers. By controlling the reaction temperature and time, fractal micro-nano structures are formed on the fiber surface. This structure not only increases the specific surface area of ​​the fiber, but also constructs a heterogeneous interface that is conducive to electromagnetic wave attenuation through multi-level pores, promoting the tight bonding between the MOF and the fiber skeleton, forming a composite fiber with both structural support and electromagnetic loss function.

[0026] After dispersing the composite fibers, freeze-setting and freeze-drying can fix the composite structure of fibers and MOFs at low temperatures, avoiding structural collapse caused by capillary shrinkage during traditional drying processes and preserving the porous properties of the aerogel. The final thermal cross-linking step further enhances the connection strength between composite fibers by unblocking the closed isocyanate groups and reacting them chemically with the fiber hydroxyl groups, forming a stable three-dimensional network structure. At the same time, it solidifies the composite morphology of MOF and fibers, ensuring the synergistic effect of structural stability and electromagnetic properties during material use. The entire process, through the combination of chemical regulation and physical molding, achieves the integrated preparation of fractal microstructure construction, in-situ MOF growth, and porous aerogel structure, providing dual structural and compositional guarantees for improved microwave absorption performance.

[0027] This invention does not impose any particular limitation on the preparation method of cellulose acetate fibers containing blocked isocyanate. Preferred preparation method is electrospinning. A preferred preparation method is as follows: cellulose acetate and polyacrylonitrile are mixed in a solvent, then blocked isocyanate is added, the mixture is stirred to obtain a spinning solution, and then electrospinning is performed to obtain cellulose acetate fibers containing blocked isocyanate. Further, the mass ratio of blocked isocyanate, cellulose acetate, and polyacrylonitrile is 1:(3~8):(0.8~1.2).

[0028] In optional embodiments of the present invention, the cellulose acetate fiber is selected from one or more of cellulose acetate fiber, cellulose diacetate fiber, or cellulose triacetate fiber; the nickel salt is selected from one or more of nickel chloride, nickel nitrate, or nickel sulfate, and in practical applications, the hydrate of the above-mentioned nickel salt can be used; other soluble nickel salts can also be selected.

[0029] In an optional embodiment of the present invention, the deacetylation treatment step is as follows: cellulose acetate fibers containing blocked isocyanates are homogenized and then placed in an alkaline solution, reacting at 20-40°C for 4-12 hours. Further, the alkaline solution is one or more of NaOH, KOH, or Ba(OH)₂ aqueous solutions, more preferably NaOH aqueous solution; the concentration of the alkaline solution is 5-30 g / L, for example, 5 g / L, 8 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, etc. The addition of the alkaline solution can efficiently catalyze the hydrolysis of acetyl groups. The present invention also includes a step of washing with water to neutrality after the deacetylation treatment.

[0030] In an optional embodiment of the present invention, the concentration of the fiber suspension is 2-10 g / L, more preferably 3-7 g / L; the solvent of the fiber suspension is water; the ratio of the fiber suspension to hexaaminotriphenyl hexahydrochloride is 10 mL : (15-120) mg, more preferably 10 mL : (20-80) mg, and even more preferably 10 mL : (30-70) mg; the molar ratio of hexaaminotriphenyl hexahydrochloride to nickel salt is 2 : (2-4), more preferably 2 : (2.5-3.5), and even more preferably 2 : (2.9-3.3).

[0031] In an optional embodiment of the present invention, in the step of adding alkaline solution after mixing and dissolving, the volume ratio of alkaline solution to fiber suspension is 1:(4~8), more preferably 1:(4~6); the alkaline solution is ammonia water, and the mass fraction of ammonia water is 23~30wt%. Ammonia water, as a weak base, can neutralize hydrochloric acid in the ligands, release free amino ligands, and simultaneously release them through OH... - Selective etching of cellulose acetate fibers by ions forms fractal microstructures on the fiber surface; however, the use of strong bases can affect the in-situ synthesis of MOFs.

[0032] In an optional embodiment of the present invention, in the step of heating to 50-90°C and stirring for a set time, the stirring time is 0.5-3 hours. This process can be carried out openly to allow sufficient oxygen to enter and promote the synthesis of MOFs. The temperature is more preferably 60-80°C, and even more preferably 65-75°C. In the present invention, the closed reaction time is 2-6 hours, and the temperature remains constant, i.e., 50-90°C, more preferably 60-80°C, and even more preferably 65-75°C. The closed reaction can be carried out in a reaction vessel. The temperature and vapor pressure are stable in the closed system, which is beneficial for promoting the orderly formation of fractal structures.

[0033] After the composite fiber is obtained by closed reaction, the present invention also includes solid-liquid separation and washing steps, wherein the solid-liquid separation is preferably filtration or vacuum filtration.

[0034] In an optional embodiment of the present invention, in the step of dispersing the composite fibers in water, the concentration of the composite fibers is 30-50 mg / mL to ensure uniform distribution of the fibers during freeze-setting, thereby obtaining an aerogel with a suitable structure and size. In the present invention, the temperature for thermal crosslinking is 100-140℃, more preferably 120-140℃, and the time is 1-6 h, more preferably 3-6 h, to ensure that the crosslinking reaction proceeds fully, forming a stable three-dimensional network structure, while simultaneously solidifying the composite morphology of MOF and fibers, ensuring the structural stability and performance durability of the aerogel during use.

[0035] This invention also provides a conductive MOF absorbing aerogel with a fractal microstructure prepared by the above-described method. The conductive MOF absorbing aerogel provided by this invention exhibits a reflection loss of -61 dB at a frequency of 13.84 GHz and an optimal effective absorption bandwidth of over 8 GHz, combining lightweight design with wideband absorption characteristics.

[0036] The present invention also provides the application of the above-mentioned conductive MOF absorbing aerogel with fractal microstructure in the field of electromagnetic wave absorption, for example, it can be used as an electromagnetic wave absorbing device.

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used. Room temperature in the following embodiments refers to 25±3℃.

[0038] In the following examples, the method for preparing cellulose acetate fibers containing blocked isocyanate is as follows: 0.9 g of polyacrylonitrile (M... W = 250,000) was dissolved in 10 mL of N,N-dimethylformamide, and 4.2 g of cellulose acetate (acetyl content 39.8wt%, hydroxyl content 3.5wt%, Mn = 40,000) was dissolved in 20 mL of N,N-dimethylformamide. 15 mL of the cellulose acetate solution was mixed with 8.75 mL of polyacrylonitrile solution, and then 1.025 g of freeze-dried aqueous blocked isocyanate (Covestro, unblocking temperature ≥90℃) was added to the mixture, and the mixture was stirred continuously for 24 hours. Electrospinning was performed using a needle with an inner diameter of 0.51 mm, and the spinning temperature was set to 40℃. The spinning parameters were as follows: positive electrode voltage 12~15 kV, negative electrode voltage -2 kV, electrode distance 25 cm, and liquid supply rate 0.48 mL / h.

[0039] Example 1 This embodiment provides a conductive MOF aerogel with fractal microstructure and its preparation method.

[0040] (1) 1g of cellulose acetate fiber containing blocked isocyanate was homogenized in a homogenizer for 20min, then 200ml of water was added to prepare a 5g / L suspension, followed by the addition of 4g NaOH. The mixture was stirred at room temperature for 6h to deacetylate, filtered and washed until neutral, to obtain the deacetylated fiber. Its transmission electron microscopy image is shown below. Figure 1 As shown, the surface of the cellulose acetate fiber was smooth before etching.

[0041] (2) The deacetylated fibers from step (1) were rehydrated to prepare a 5 g / L fiber suspension. Then, hexaaminotriphenylene hexahydrochloride and nickel nitrate hexahydrate were added, wherein the ratio of the fiber suspension to hexaaminotriphenylene hexahydrochloride was controlled to be 10 mL : 64.45 mg, and the molar ratio of hexaaminotriphenylene hexahydrochloride to nickel nitrate hexahydrate was 2:3. After complete dissolution, 25 wt% ammonia water was added, and the volume ratio of the fiber suspension to ammonia water was controlled to be 10 mL : 1.8 mL. The mixture was stirred for 30 min. Then, it was heated to 70 °C, stirred openly for 2 h, and then stirred sealed for 4 h to obtain a conductive MOF anchoring composite fiber with a fractal structure.

[0042] (3) The obtained conductive MOF anchoring composite fiber with fractal structure was filtered, washed with water until neutral, resuspended in water and stirred thoroughly to obtain a suspension, and the concentration of composite fiber was controlled to be 40 mg / mL. Then the suspension was injected into a liquid nitrogen mold for freezing and shaping, and then freeze-dried in a freeze dryer to obtain an aerogel. The obtained aerogel was thermally crosslinked at 135°C for 4 h to obtain a conductive MOF aerogel with fractal microstructure.

[0043] Transmission electron microscopy (TEM) images of the conductive MOF aerogel with fractal microstructure prepared in this embodiment are shown below. Figure 2 As shown, secondary fractal fibers are clearly visible; scanning electron microscope images are as follows. Figure 3 As shown in the figure, the surface of the fiber grown in situ by etching in this embodiment is rough and uniform, and no agglomeration phenomenon is observed.

[0044] To demonstrate the etching effect of ammonia, the deacetylated fibers obtained in step (1) were mixed with water to prepare a fiber suspension of 5 g / L. Then, 25 wt% ammonia was added, controlling the volume ratio of the fiber suspension to ammonia to be 10 mL : 1.8 mL. The mixture was stirred for 30 min, then heated to 70 °C and stirred openly for 2 h, followed by stirring in a sealed container for 4 h. The mixture was then filtered, washed with water until neutral, dried, and its scanning electron microscope image was obtained. Figure 4 As shown, the surface of the cellulose acetate fiber after etching exhibits a dissolved morphology.

[0045] Example 2 This embodiment provides a conductive MOF aerogel with fractal microstructure and its preparation method.

[0046] (1) Place 1g of cellulose acetate fiber containing blocked isocyanate into a homogenizer and homogenize for 20min. Then prepare a 200mL 5g / L suspension. Add 4g NaOH and stir at room temperature for 6h to deacetylate. Filter and wash until neutral to obtain the deacetylated fiber.

[0047] (2) The deacetylated fibers from step (1) were rehydrated to prepare a 5 g / L fiber suspension. Then, hexaaminotriphenylene hexahydrochloride and nickel nitrate hexahydrate were added, wherein the ratio of the fiber suspension to hexaaminotriphenylene hexahydrochloride was controlled to be 10 mL : 34.7 mg, and the molar ratio of hexaaminotriphenylene hexahydrochloride to nickel nitrate hexahydrate was 2:3. After complete dissolution, 25 wt% ammonia water was added, and the volume ratio of the fiber suspension to ammonia water was controlled to be 10 mL : 1.8 mL. The mixture was stirred for 30 min. Then, it was heated to 70 °C, stirred openly for 2 h, and then stirred sealed for 4 h to obtain a conductive MOF anchoring composite fiber with a fractal structure.

[0048] (3) The obtained conductive MOF anchoring composite fiber with fractal structure was filtered, washed with water until neutral, resuspended in water and stirred thoroughly to obtain a suspension, and the concentration of composite fiber was controlled to be 40 mg / mL. Then the suspension was injected into a liquid nitrogen mold for freezing and shaping, and then freeze-dried in a freeze dryer to obtain an aerogel. The obtained aerogel was thermally crosslinked at 135°C for 4 h to obtain a conductive MOF aerogel with fractal microstructure.

[0049] Example 3 This embodiment provides a conductive MOF aerogel with fractal microstructure and its preparation method.

[0050] (1) Place 1g of cellulose acetate fiber containing blocked isocyanate into a homogenizer and homogenize for 20min. Then add 200ml of water to prepare a 5g / L suspension. Then add 4g of NaOH and stir at room temperature for 6h to deacetylate. Filter and wash until neutral to obtain the deacetylated fiber.

[0051] (2) The deacetylated fibers from step (1) were rehydrated to prepare a 5 g / L fiber suspension. Then, hexaaminotriphenylene hexahydrochloride and nickel sulfate hexahydrate were added, wherein the ratio of the fiber suspension to hexaaminotriphenylene hexahydrochloride was controlled to be 10 mL : 64.45 mg, and the molar ratio of hexaaminotriphenylene hexahydrochloride to nickel sulfate hexahydrate was 2:3. After complete dissolution, 25 wt% ammonia water was added, and the volume ratio of the fiber suspension to ammonia water was controlled to be 10 mL : 1.8 mL. The mixture was stirred for 30 min. Then, it was heated to 70 °C, stirred openly for 2 h, and then stirred sealed for 4 h to obtain a conductive MOF anchoring composite fiber with a fractal structure.

[0052] (3) The obtained conductive MOF anchoring composite fiber with fractal structure was filtered, washed with water until neutral, resuspended in water and stirred thoroughly to obtain a suspension, and the concentration of composite fiber was controlled to be 40 mg / mL. Then the suspension was injected into a liquid nitrogen mold for freezing and shaping, and then freeze-dried in a freeze dryer to obtain an aerogel. The obtained aerogel was thermally crosslinked at 135°C for 4 h to obtain a conductive MOF aerogel with fractal microstructure.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example did not involve in-situ growth of the MOF; instead, the conductive MOF and the deacetylated fiber were directly mixed. The steps of this comparative example are as follows: (1) Place 1g of cellulose acetate fiber containing blocked isocyanate into a homogenizer and homogenize for 20min. Then add 200ml of water to prepare a 5g / L suspension. Then add 4g of NaOH and stir at room temperature for 6h to deacetylate. Filter and wash until neutral to obtain the deacetylated fiber.

[0054] (2) Take 20 mL of deionized water and add hexaaminotriphenyl hexahydrochloride and nickel nitrate hexahydrate to it. The ratio of water to hexaaminotriphenyl hexahydrochloride is controlled at 10 mL : 64.45 mg, and the molar ratio of hexaaminotriphenyl hexahydrochloride to nickel nitrate hexahydrate is 2:3. After complete dissolution, add 25 wt% ammonia water, controlling the volume ratio of the solution to the added ammonia water to 10 mL : 1.8 mL, and stir for 30 min. Then heat to 70 °C, stir open for 2 h, then seal and stir for 4 h. Afterward, centrifuge three times and dry in a 50 °C oven to obtain conductive MOF (Ni-HITP) powder.

[0055] (3) The deacetylated fiber in step (1) was rehydrated to prepare a fiber suspension with a fiber concentration of 20 mg / mL. Then, the MOF powder synthesized in (2) was added to the suspension and its concentration was controlled to be 20 mg / mL. After mixing evenly, it was injected into a liquid nitrogen mold for freezing and shaping. Then, it was freeze-dried by a freeze dryer to obtain an aerogel. The obtained aerogel was thermally crosslinked at 135°C for 4 h to obtain a simple mixed conductive MOF aerogel.

[0056] Figure 5 The image shows a scanning electron microscope (SEM) image of the simple mixed conductive MOF aerogel prepared in this comparative example. It can be seen that the aerogel prepared by simple mixing exhibits obvious agglomeration on the surface and has poor uniformity.

[0057] Test case 1. Pore structure determination Figure 6The BET micro-mesopore size distribution (A) and mercury porosimetry macropore size distribution (B) of the conductive MOF aerogel with fractal microstructure prepared in Example 1 and the simple mixed conductive MOF aerogel of Comparative Example 1 are shown. It can be seen that the conductive MOF aerogel with fractal microstructure prepared in Example 1 has more pore structures than the aerogel of Comparative Example 1, and has a three-level pore structure from micropores to mesopores to macropores.

[0058] 2. X-ray diffraction (XRD) pattern Figure 7 The XRD patterns of untreated cellulose acetate fibers, conductive MOF (Ni-HITP) powder obtained in step (2) of Comparative Example 1, conductive MOF aerogel with fractal microstructure of Example 1, and simple mixed conductive MOF aerogel of Comparative Example 1 show that the peak position of conductive MOF aerogel with fractal microstructure of Example 1 is blunted compared with Comparative Example 1, while the peak position remains basically unchanged.

[0059] 3. Characterization of mechanical properties Figure 8 The load-bearing capacity of the conductive MOF aerogel with fractal microstructure prepared in Example 1 under 1000 times the pressure (1000 times the weight of the aerogel itself) and macroscopic photographs when placed on foxtail grass. Figure 8 A) and compression performance cycle ( Figure 8 (B in the text). It can be seen that the prepared aerogel has both lightweight and high strength characteristics.

[0060] 4. Structural stability determination The conductive MOF aerogel with fractal microstructure prepared in Example 1 was soaked in water for seven days and then dried in air. Figure 9 As shown in the figure, the aerogel structure did not collapse after being re-dried, indicating that it has good structural stability.

[0061] 5. Electromagnetic absorption performance test Figure 10 The dielectric constant diagrams are shown for the conductive MOF absorbing aerogel with fractal microstructure in Example 1 and the conductive MOF absorbing aerogel in Comparative Example 1. Figure 11 The diagram shows the reflection loss performance of the conductive MOF absorbing aerogel with fractal microstructure in Example 1 and the conductive MOF absorbing aerogel in Comparative Example 1.

[0062] from Figure 10 and Figure 11As can be seen, compared with simply mixed conductive MOF aerogels, the obtained conductive MOF aerogels with fractal microstructures have excellent electromagnetic parameters and possess the potential to be excellent electromagnetic wave absorbing materials. The conductive MOF aerogel absorbing material with fractal microstructures exhibits excellent electromagnetic wave absorption performance. At a frequency of 13.84 GHz, the reflection loss to electromagnetic waves reaches -61 dB, with a matching thickness of only 3.49 mm, and the optimal effective absorption bandwidth reaches 8.32 GHz.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a conductive MOF absorbing aerogel with a fractal microstructure, characterized in that, Includes the following steps: Cellulose acetate fibers containing blocked isocyanates are deacetylated and then made into fiber suspensions. Hexaaminotriphenyl hexahydrochloride and nickel salt were added to the fiber suspension, mixed and dissolved, and then an alkaline solution was added. The temperature was then raised to 50-90°C and stirred for a set time before being sealed for reaction to obtain composite fiber. The composite fibers are dispersed in water and then subjected to freeze-setting, freeze-drying and thermal cross-linking in sequence to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The cellulose acetate fiber is selected from one or more of cellulose acetate fiber, cellulose diacetate fiber, or cellulose triacetate fiber; the nickel salt is selected from one or more of nickel chloride, nickel nitrate, or nickel sulfate.

3. The preparation method according to claim 1, characterized in that, The deacetylation treatment step is as follows: homogenize cellulose acetate fibers containing blocked isocyanate and place them in an alkaline solution, reacting at 20~40℃ for 4~12h.

4. The preparation method according to claim 3, characterized in that, The alkaline solution is one or more of NaOH, KOH or Ba(OH)2 aqueous solution, and the concentration of the alkaline solution is 5~30 g / L.

5. The preparation method according to claim 1, characterized in that, The concentration of the fiber suspension is 2~10 g / L, and the solvent is water; the ratio of the fiber suspension to hexaaminotriphenyl hexahydrochloride is 10 mL : (15~120) mg; the molar ratio of hexaaminotriphenyl hexahydrochloride to nickel salt is 2 : (2~4).

6. The preparation method according to claim 1, characterized in that, In the step of adding alkali solution after mixing and dissolving, the volume ratio of alkali solution to fiber suspension is 1:(4~8); the alkali solution is ammonia water with a mass fraction of 23~30wt%.

7. The preparation method according to claim 1, characterized in that, In the step of heating to 50~90℃ and stirring for a set time, the stirring time is 0.5~3h; the time of the sealed reaction is 2~6h.

8. The preparation method according to claim 1, characterized in that, In the step of dispersing the composite fiber in water, the concentration of the composite fiber is 30~50 mg / mL; the temperature of the thermal crosslinking is 100~140℃ and the time is 1~6 h.

9. The conductive MOF aerogel with fractal microstructure prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the conductive MOF absorbing aerogel with fractal microstructure as described in claim 9 in the field of electromagnetic wave absorption.

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