A cnt / mof composite hydrogel

Abstract

This invention provides a hydrogel in which zirconium-based MOFs are dispersed; the zirconium-based MOFs are loaded with carbon nanotubes coated with polydopamine; the organic ligand of the zirconium-based MOFs is 2-aminoterephthalic acid; and unsaturated metal sites are present in the zirconium-based MOFs. The CNT / MOF composite hydrogel provided by this invention achieves a synergistic enhancement of multiple properties through the synergistic combination of dopamine-modified CNTs, MOFs, and the hydrogel. This synergistic effect, while retaining the lightweight properties of the material, achieves multifunctional integration of electromagnetic protection, mechanical strain, and sensing performance, perfectly meeting the application requirements of new electronic devices and effectively solving the problem of unbalanced comprehensive performance of existing materials.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials, specifically relating to a CNT / MOF composite hydrogel with microwave absorbing function, its preparation method, and its application. Background Technology

[0002] With the rapid development of science and technology, high-tech electronic products such as smart wearables and electronic packaging are widely used, and traditional microwave absorbing materials can no longer meet the ever-increasing performance requirements. Therefore, smart sensing microwave absorbing materials with flexible and high-strain properties have become an important research direction.

[0003] Hydrogels possess excellent flexibility and biocompatibility, but their intrinsic conductivity is low, impedance matching capability is limited, and their loss capacity is weak when used alone as a microwave absorbing material. Therefore, they are usually used as flexible matrices and combined with conductive / dielectric fillers to construct composite materials that combine flexibility and microwave absorption functions. Patent CN114399271A discloses a method for preparing a high-strength and tough physical hydrogel, using polyvinyl alcohol (PVA), tannic acid-Fe... 3+ Co-flocculation with complexes achieved high strength (6.5 MPa) and high toughness in the hydrogel. This material shows significant potential for application in flexible electronics and biomimetic materials, but its long-term stability and functional expansion (such as conductivity and electromagnetic wave absorption properties) still require further investigation.

[0004] MOFs are a class of crystalline porous materials assembled from metal ions or clusters and organic ligands. Based on their ordered pore structure, large specific surface area and tunable topology, they have been widely studied in fields such as gas adsorption, catalysis and energy.

[0005] Patent CN115537180A discloses a two-dimensional conductive MOF (Metal-Oxide-Foil) absorbing material, its preparation method, and its applications. This invention obtains the two-dimensional conductive MOF absorbing material by reacting a metal salt solution with a solution of 2,3,6,7,10,11-hexaaminotriphenylhexahydrochloride. This material possesses a layered porous structure and suitable conductivity, achieving good electromagnetic wave absorption performance (minimum reflection loss of -28.5 dB). However, compared with subsequently developed carbon-based superstructure absorbing materials, the absorption performance of this MOF material still lags behind, and its mechanical flexibility is insufficient, making it difficult to directly meet the needs of flexible wearable devices. To further improve the electromagnetic wave absorption performance of MOFs, they are often composited with other materials, utilizing synergistic effects to introduce multiple loss mechanisms, effectively enhancing the dielectric loss capability of the MOF to achieve efficient electromagnetic wave absorption.

[0006] Carbon nanotubes (CNTs) are often used in electromagnetic wave absorbing materials due to their light weight, high electrical conductivity, large aspect ratio and specific surface area, stable chemical properties, and outstanding tunability of microstructure.

[0007] Patent CN118894523A discloses a method for preparing a superstructured carbon nanotube (CNT) microwave absorbing material. Using a MoO3 nanorod template method and a polyimide carbonization process, a microwave absorbing material with an ordered mesoporous structure and good dispersion is prepared, achieving a minimum reflection loss of -66.0 dB and an effective absorption bandwidth of 12.6 GHz (5.4-18.0 GHz). It should be noted that these superior properties typically rely on a carefully designed superstructure or specific morphology. Ordinary carbon nanotubes have poor impedance matching and an inert surface, resulting in poor compatibility with matrix materials such as MOFs and hydrogels. Direct composite formation easily leads to agglomeration, resulting in weak interfacial bonding within the material. This not only fails to fully utilize the synergistic effect between MOFs and CNTs but also affects the mechanical properties and microwave absorption stability of the composite material.

[0008] In existing technologies, high-strength and tough hydrogels lack efficient electromagnetic loss capabilities; MOF absorbing materials lack sufficient mechanical flexibility; and high-performance carbon nanotube structures have poor compatibility with polar matrices. Currently, there is a lack of composite material systems that can simultaneously achieve flexibility, mechanical strength, and broadband strong absorption characteristics. Therefore, before compositing CNTs with MOFs or hydrogels, a CNT surface modification step is usually required. This involves improving the surface activity, dispersibility, and compatibility with the matrix material through chemical or physical modifications, thereby enhancing the mechanical strength, flexibility, and stability of the composite material's microwave absorption performance. This lays the foundation for the subsequent construction of high-performance flexible microwave absorbing composite materials.

[0009] Developing efficient electromagnetic shielding materials has become a problem that needs to be solved in the field of materials science. Electromagnetic shielding materials not only need to have excellent electromagnetic wave absorption performance, but also need to have good mechanical strain characteristics to adapt to complex usage environments (such as flexible wearable devices, deformable electronic devices, etc.). However, traditional absorbing materials are often hard and have poor flexibility, making it difficult to meet this comprehensive performance requirement. Summary of the Invention

[0010] To address the aforementioned technical bottlenecks, this invention provides a composite hydrogel that combines lightweight properties, high-efficiency electromagnetic protection performance, and good strain sensing performance.

[0011] This invention is achieved through the following technical solution: A hydrogel in which zirconium-based MOFs are dispersed; The zirconium-based MOFs are loaded with carbon nanotubes coated with polydopamine. The organic ligand of the zirconium-based MOFs is 2-aminoterephthalic acid; The zirconium-based MOFs contain unsaturated metal sites.

[0012] The method for preparing the hydrogel includes the following steps: Carbon nanotubes were dispersed in an alkaline Tris-HCl buffer solution, then dopamine salt was added, the reaction was carried out and the mixture was separated to obtain carbon nanotubes coated with polydopamine. Zirconium salt, ionic liquid and 2-aminoterephthalic acid were dissolved in an organic solvent, glacial acetic acid was added to react, and then carbon nanotubes coated with polydopamine were added and subjected to hydrothermal reaction to obtain zirconium-based MOFs loaded with carbon nanotubes coated with polydopamine. Zirconium-based MOFs loaded with carbon nanotubes coated with polydopamine and a dispersant were mixed in water to obtain solution A; The pore-forming agent and initiator are mixed with water to obtain solution B; Solution A, N,N'-methylenebisacrylamide, and acrylamide were added to solution B and mixed to obtain an emulsion, which was then reacted to obtain the final product. The ionic liquid is Where 2≤m≤10, X includes Cl - .

[0013] The pH value of the Tris-HCl buffer solution is 8-9.

[0014] The mass ratio of dopamine salt to CNT is 1:2 to 1:5.

[0015] The separation includes centrifugal separation; The centrifugation speed is 8000-10000 r / min.

[0016] The organic solvent includes N,N-dimethylformamide; The molar ratio of zirconium salt, ionic liquid, and 2-aminoterephthalic acid is 4:0.1-0.3:4. The hydrothermal reaction temperature is 100-140℃. The amount of glacial acetic acid added is 12.5-25 mL per 1 mol of zirconium salt; Carbon nanotubes coated with polydopamine account for 20-40% of the total mass. The content of zirconium-based MOFs loaded with polydopamine-coated carbon nanotubes in solution A is 0.0025 g / mL; The dispersant content in solution A is 0.00075 g / mL.

[0017] The dispersant is sodium carboxymethyl cellulose.

[0018] In solution B, the content of pore-forming agent is 0.00075 g / mL; In solution B, the initiator concentration is 0.00075 g / mL; The pore-forming agent is ammonium bicarbonate; The initiator is potassium persulfate; The emulsion contains 0.00025 g / mL of N,N'-methylenebisacrylamide. The acrylamide content in the emulsion is 0.025 g / mL.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a CNT / MOF composite hydrogel that achieves synergistic enhancement of multiple properties through the synergistic combination of dopamine-modified CNTs, MOFs, and hydrogels: First, dopamine-modified CNTs improve interfacial compatibility with MOFs and hydrogels, preventing CNT aggregation. Simultaneously, the polydopamine coating layer forms a conductive-dielectric synergistic loss with the CNTs, significantly improving microwave absorption performance. Second, the modified CNTs act as a "connecting bridge," synergizing the porous characteristics of MOFs and the flexibility of hydrogels to significantly enhance the mechanical strength, flexibility, and stability of the composite system, making it suitable for flexible applications. Third, the unsaturated metal ions alter the polarization. These three synergistic effects, while retaining the lightweight properties of the material, achieve multifunctional integration of electromagnetic protection, mechanical strain, and sensing performance, perfectly meeting the application requirements of new electronic devices and effectively solving the problem of unbalanced overall performance of existing materials. Attached Figure Description

[0020] Figure 1 The images show the SEM images of PCNT / MOF-1 prepared in Example 1, as well as the microwave absorption properties, tensile test results, and strain sensing performance of the PCNT / MOF-1 composite hydrogel. Figure 1 (a) is a SEM image of PCNT / MOF-1, which shows that the carbon nanotube surface is coated with a large number of hexahedral MOFs; Figure 1 (b) and (c) are the three-dimensional and two-dimensional reflection loss diagrams of the PCNT / MOF-1 composite hydrogel, with a minimum reflection loss of -31.68 dB and an effective absorption bandwidth of 2.478 GHz.

[0021] Figure 1 (d) is the stress-strain diagram of the PCNT / MOF-1 composite hydrogel, with a tensile strength of 18.45 MPa and an elongation at break of 1039.4%, exhibiting excellent flexibility and mechanical properties. Figure 1 (e) is the resistance sensing signal generated by the PCNT / MOF-1 composite hydrogel as the wrist is bent. The signal intensity is high and the resistance change rate reaches 4.6.

[0022] Figure 2 The images show the SEM images of PCNT / MOF-2 prepared in Example 2, as well as the microwave absorption properties, tensile test results, and strain sensing performance of the PCNT / MOF-2 composite hydrogel. Figure 2 (a) is a SEM image of PCNT / MOF-2, which shows that the number of hexahedral MOFs coating the surface of carbon nanotubes has decreased. Figure 2 (b) and (c) are the three-dimensional and two-dimensional reflection loss diagrams of the PCNT / MOF-2 composite hydrogel, with a minimum reflection loss (RL) of -54.74 dB and an effective absorption bandwidth (EAB) of 2.94 GHz.

[0023] Figure 2 (d) is the stress-strain diagram of the PCNT / MOF-2 composite hydrogel, with a tensile strength of 18.8 MPa and an elongation at break of 1109.8%, exhibiting excellent flexibility and mechanical properties.

[0024] Figure 2 (e) is the resistance sensing signal generated by the PCNT / MOF-1 composite hydrogel as the wrist is bent. The signal intensity is increased and the resistance change rate reaches 6.1.

[0025] Figure 3 The images show the SEM images of PCNT / MOF-3 prepared in Example 3, as well as the microwave absorption properties, tensile test results, and strain sensing performance of the PCNT / MOF-3 composite hydrogel. Figure 3 (a) is a SEM image of PCNT / MOF-3, which shows that the number of hexahedral MOFs coating the surface of carbon nanotubes has decreased. Figure 3 (b) and (c) are the three-dimensional and two-dimensional reflection loss diagrams of the PCNT / MOF-3 composite hydrogel, with a minimum reflection loss of -28.1 dB and an effective absorption bandwidth of 2.814 GHz.

[0026] Figure 3 (d) is the stress-strain diagram of the PCNT / MOF-3 composite hydrogel, with a tensile strength of 14.9 MPa and an elongation at break of 960.6%, exhibiting excellent flexibility and mechanical properties.

[0027] Figure 3 (e) is the resistance sensing signal generated by the PCNT / MOF-3 composite hydrogel as the wrist is bent. The signal intensity is high and the resistance change rate reaches 4.1.

[0028] Figure 4 The images shown are TEM and XPS images of the PCNT obtained in Example 2. Figure 4 (a) is a TEM image of PCNT. From Figure 4 A distinct dopamine coating can be seen on the surface of CNTs. Figure 4(b) is the XPS plot of PCNT. As can be seen from the plot, compared with the XPS of CNT, the XPS of PCNT shows N1s and O1s peaks after being coated with dopamine, which are due to the amino and phenolic hydroxyl groups in dopamine.

[0029] Figure 5 The following is an XPS diagram of zirconium elements in the MOFs prepared in step 4 of Example 1.

[0030] Figure 6 The zirconium element XPS plot of the MOFs prepared in step 4 of Comparative Example 4 is shown. Detailed Implementation

[0031] This invention provides a method for preparing a CNT / MOF composite hydrogel, which includes the following steps: Carbon nanotubes (CNTs) were dispersed in an alkaline Tris-HCl buffer solution using ultrasonic power, and then dopamine hydrochloride was added. The mixture was stirred and reacted at room temperature in the dark to polymerize dopamine, yielding polydopamine-coated CNTs (PCNTs). At this point, the PCNTs were dispersed in the mixture. To separate the PCNTs from the mixture, the first mixture was centrifuged, the precipitate was collected, and the precipitate was washed alternately with deionized water and anhydrous ethanol, then vacuum dried. The dopamine coating layer contains a large number of active functional groups such as amino and hydroxyl groups, which can effectively overcome the inertness of the CNT surface and prevent aggregation when directly composited with MOFs and hydrogels in subsequent steps. Simultaneously, these active functional groups can form hydrogen bonds with hydrophilic groups in the hydrogel matrix, significantly enhancing the interfacial bonding between CNTs and the composite system in subsequent steps and improving the interfacial compatibility between heterogeneous phases.

[0032] Water-soluble zirconium salts and ionic liquids (Published in Chinese patent application CN1850802A) 2-Aminoterephthalic acid was dissolved in an organic solvent; after ultrasonic dissolution, glacial acetic acid was added while stirring, followed by the addition of PCNT and stirring; a second mixed system was obtained. The second mixed system was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 100-140°C. After cooling, the mixture was filtered, washed twice with DMF, and once with methanol. After washing, it was vacuum dried to obtain PCNT-loaded MOFs (MOFs / PCNT). In this step, zirconium ions react with 2-aminoterephthalic acid to form metal-organic framework compounds (MOFs); however, the cation in the ionic liquid contains an amide, and the oxygen in the amide can coordinate with zirconium ions, thereby interfering with the reaction between zirconium ions and 2-aminoterephthalic acid, thus forming unsaturated metal sites. Zirconium ions were chosen because they have four positive charges, making them prone to unsaturation. This ionic liquid was chosen because it is relatively easy to remove after the reaction, and its coordination ability is moderate, preventing excessive unsaturation of metal ions after the reaction, which would affect the absorption performance. Ligand deficiency or unsaturation of the metal center introduces dipole polarization and interfacial polarization, promoting electromagnetic wave energy dissipation. While dipole polarization is a frequency-dependent relaxation process, excessively strong dipole polarization, leading to an excessively high dielectric constant, may disrupt impedance matching and reduce absorption efficiency. Therefore, using an ionic liquid with relatively weak coordination ability avoids excessive unsaturation of zirconium ions. Furthermore, polydopamine itself possesses excellent dielectric properties, and its coating layer can form additional dielectric loss sites on the CNT surface, creating a synergistic effect with the CNT's own conductivity loss. This significantly optimizes the electromagnetic wave absorption efficiency and shielding performance of the composite hydrogel, overcoming the shortcomings of insufficient conductivity and poor electromagnetic protection performance of existing flexible hydrogels, thus achieving highly efficient electromagnetic protection. Although carbon nanotubes themselves are primarily responsible for conductive losses, the dipole polarization and interfacial polarization of unsaturated zirconium ions in MOFs can induce carbon nanotube polarization, leading to dipole polarization relaxation under an applied electromagnetic field and consuming electromagnetic energy. Furthermore, MOFs form interfaces with polydopamine; polydopamine also forms interfaces with carbon nanotubes. These multiple interfaces enhance the synergistic effect between the polarization loss centers and the dipole polarization of the carbon nanotubes themselves, thereby broadening the absorption bandwidth and reducing reflection loss.

[0033] 0.1-0.2 g of sodium carboxymethyl cellulose (CMC-Na), a dispersant for MOFs / PCNTs, was added to deionized water and stirred to obtain solution A. Pore-forming agent NH4HCO3 and thermal initiator potassium persulfate (KPS) were dissolved in deionized water to obtain solution B. Solution A, MBA, and AAM were thoroughly mixed with solution B and stirred to obtain a uniformly dispersed emulsion. The resulting emulsion was transferred to a mold for reaction, ultimately yielding the MOF / CNT composite hydrogel.

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Example 1 This embodiment provides a method for synthesizing PCNT / MOF composite hydrogel materials using a simple solvent method. The specific process is as follows: Step 1: Disperse CNTs in Tris-HCl buffer at pH 8.5 using sonication for 60 min.

[0036] Step 2: Add dopamine hydrochloride, controlling the mass ratio of dopamine hydrochloride to CNT to be 1:3, and stir the reaction for 24 hours at room temperature and in the dark.

[0037] Step 3: Place the mixture in a centrifuge and centrifuge at 8000 r / min for 10 min. Collect the precipitate, wash it three times alternately with deionized water and anhydrous ethanol, and dry it under vacuum at 60℃ for 24 h to obtain polydopamine-coated modified CNTs, named PCNT.

[0038] Step 4: Add 0.4 mmol and 0.01 mmol of zirconium tetrachloride ionic liquid (m=3, X is Cl) - 0.4 mmol of 2-aminoterephthalic acid was dissolved in 40 mL of N,N-dimethylformamide (DMF). After sonication to dissolve, 8 mL of glacial acetic acid was added while stirring. Then, 20% of the total mass of PCNT was added and stirred for 1 h.

[0039] Step 5: Transfer the solution obtained in Step 1 to a 100ml hydrothermal reactor and react it at 120℃ for 12h. After cooling, filter it, wash it twice with DMF and once with methanol, and then vacuum dry it at 80℃ for 12h. The obtained sample is named PCNT / MOF-1.

[0040] Step 6: Add 0.1g of PMOF / CNT-1 and 0.03g of dispersant sodium carboxymethyl cellulose (CMC-Na) to 40 mL of deionized water and stir for 1 h to obtain solution A.

[0041] Step 7: Add 0.03g of pore-forming agent NH4HCO3 and 0.03g of thermal initiator potassium persulfate (KPS) to 40 mL of deionized water and dissolve for 1 hour to obtain solution B.

[0042] Step 8: Add solution A, solution B, 0.01g MBA and 1g AAM to the solution and mix thoroughly. Stir for 2 hours to obtain a uniformly dispersed emulsion.

[0043] Step 9: Transfer the emulsion obtained in step 5 into a mold and react at 80°C for 2 hours to finally obtain PCNT / MOF-1 hydrogel.

[0044] The prepared PCNT / MOF-1 hydrogel absorbing material has a minimum reflection loss of -31.68B and an effective absorption bandwidth of 2.478GHz. It exhibits a tensile strength of 18.45MPa, an elongation at break of 1039.4%, and a sensing resistance change rate of 4.6.

[0045] Example 2 This embodiment provides a method for synthesizing PCNT / MOF composite hydrogel materials using a simple solvent method. The specific process is as follows: Step 1: Disperse CNTs in Tris-HCl buffer at pH 8.5 using sonication for 60 min.

[0046] Step 2: Add dopamine hydrochloride, controlling the mass ratio of dopamine hydrochloride to CNT to be 1:3, and stir the reaction for 24 hours at room temperature and in the dark. Step 3: Place the mixture in a centrifuge and centrifuge at 8000 r / min for 10 min. Collect the precipitate, wash it three times alternately with deionized water and anhydrous ethanol, and dry it under vacuum at 60℃ for 24 h to obtain polydopamine-coated modified CNTs, named PCNT. Step 4: Add 0.4 mmol and 0.02 mmol of zirconium tetrachloride ionic liquid (m=5, X is Cl) - 0.4 mmol of 2-aminoterephthalic acid was dissolved in 40 mL of N,N-dimethylformamide (DMF). After sonication to dissolve, 8 mL of glacial acetic acid was added while stirring. Then, 30% of the total mass of PCNT was added and stirred for 1 h.

[0047] Step 5: Transfer the solution obtained in Step 1 to a 100ml hydrothermal reactor and react it at 120℃ for 12 h. After cooling, filter the solution, wash it twice with DMF and once with methanol, and then vacuum dry it at 80℃ for 12 h. The obtained sample is named PCNT / MOF-2.

[0048] Step 6: Add 0.1 g of PCNT / MOF-2 and 0.03 g of dispersant sodium carboxymethyl cellulose (CMC-Na) to 40 mL of deionized water and stir for 1 h to obtain solution B.

[0049] Step 7: Dissolve 0.03 g of pore-forming agent NH4HCO3 and 0.03 g of thermal initiator potassium persulfate (KPS) in 40 mL of deionized water for 1 hour.

[0050] Step 8: Add the solution A obtained in step 3, 0.01g MBA and 1g AAM to the solution and mix thoroughly. Stir for 2 hours to obtain a uniformly dispersed emulsion.

[0051] Step 9: Transfer the emulsion obtained in step 5 into a mold and react at 80°C for 2 h to finally obtain PCNT / MOF-2 hydrogel.

[0052] The prepared PCNT / MOF-2 hydrogel absorbing material exhibits a minimum reflection loss (RL) of -54.74 dB and an effective absorption bandwidth (EAB) of 2.94 GHz at a thickness of 2.04 mm. It also demonstrates a tensile strength of 18.8 MPa, an elongation at break of 1109.8%, and a sensing resistance change rate of 6.1%.

[0053] Example 3 This embodiment provides a method for synthesizing PCNT / MOF composite hydrogel materials using a simple solvent method. The specific process is as follows: Step 1: Disperse CNTs in Tris-HCl buffer at pH 8.5 using sonication for 60 min.

[0054] Step 2: Add dopamine hydrochloride, controlling the mass ratio of dopamine hydrochloride to CNT to be 1:2, and stir the reaction for 2 h at room temperature and in the dark.

[0055] Step 3: Place the mixture in a centrifuge and centrifuge at 8000 r / min for 10 min. Collect the precipitate, wash it three times alternately with deionized water and anhydrous ethanol, and dry it under vacuum at 60℃ for 24 h to obtain polydopamine-coated modified CNTs, named PCNT.

[0056] Step 4: Add 0.4 mmol and 0.03 mmol of zirconium tetrachloride ionic liquid (m=7, X is Cl) - 0.4 mmol of 2-aminoterephthalic acid was dissolved in 40 mL of N,N-dimethylformamide (DMF). After sonication to dissolve, 8 mL of glacial acetic acid was added while stirring. Then, 30% of the total mass of PCNT was added and stirred for 1 h.

[0057] Step 5: Transfer the solution obtained in Step 1 to a 100 ml hydrothermal reactor and react it at 120℃ for 12 h. After cooling, filter the solution, wash it twice with DMF and once with methanol, and then vacuum dry it at 80℃ for 12 h. The resulting sample is named PCNT / MOF-3.

[0058] Step 6: Add 0.15g PCNT / MOF-3 and 0.03g sodium carboxymethyl cellulose (CMC-Na) dispersant to 40 mL of deionized water and stir for 1 h to obtain solution B.

[0059] Step 7: Dissolve 0.03g of pore-forming agent NH4HCO3 and 0.03g of thermal initiator potassium persulfate (KPS) in 40 mL of deionized water for 1 hour.

[0060] Step 8: Add solution A obtained in step 3, 0.01g MBA and 1g AAM to the solution and mix thoroughly. Stir for 2 hours to obtain a uniformly dispersed emulsion. Step 9: Transfer the emulsion obtained in step 5 into a mold and react at 80°C for 2 h to finally obtain PCNT / MOF-3 hydrogel.

[0061] The prepared PCNT / MOF-3 hydrogel absorbing material has a minimum reflection loss of -28.1 dB and an effective absorption bandwidth of 2.814 GHz. It exhibits a tensile strength of 14.9 MPa, an elongation at break of 960.6%, and a sensing resistance change rate of 4.1%.

[0062] Comparative Example 1: This comparative example presents a MOF composite hydrogel (without carbon nanotubes), the specific process of which is as follows: Step 1: Dissolve 0.4 mmol of zirconium tetrachloride and 0.4 mmol of 2-aminoterephthalic acid in 40 mL of N,N-dimethylformamide (DMF), sonicate to dissolve, and then add 8 mL of glacial acetic acid while stirring.

[0063] Step 2: Transfer the solution obtained in Step 1 to a 100 ml hydrothermal reactor and react it at 120℃ for 12 h. After cooling, filter the solution, wash it twice with DMF and once with methanol, and then dry it under vacuum at 80℃ for 12 h. The resulting sample is named MOF.

[0064] Step 3: Add 0.1 g MOF and 0.03 g dispersant sodium carboxymethyl cellulose (CMC-Na) to 40 mL of deionized water and stir for 1 h to obtain solution B.

[0065] Step 4: Dissolve 0.03g of pore-forming agent NH4HCO3 and 0.03g of thermal initiator potassium persulfate (KPS) in 40 mL of deionized water for 1 h.

[0066] Step 5: Add the solution A obtained in step 3, 0.01g MBA and 1g AAM to the solution and mix thoroughly. Stir for 2 hours to obtain a uniformly dispersed emulsion.

[0067] Step 6: Transfer the emulsion obtained in step 5 into a mold and react at 80°C for 2 hours to finally obtain MOF hydrogel.

[0068] The prepared MOF hydrogel exhibits a reflection loss (RL) greater than -10 dB across the entire X-ray band, demonstrating almost no ability to absorb electromagnetic waves. Its tensile strength is 6.8 MPa, and its elongation at break is 1210.1%.

[0069] Comparative Example 2 This comparative example provides a MOF composite hydrogel (without carbon nanotube coating), the specific process of which is as follows: Step 1: Dissolve 0.4 mmol of zirconium tetrachloride and 0.4 mmol of 2-aminoterephthalic acid in 40 mL of N,N-dimethylformamide (DMF). After sonication to dissolve, add 8 mL of glacial acetic acid while stirring. Then add 30% of the total mass of CNT and stir for 1 h.

[0070] Step 2: Transfer the solution obtained in Step 1 to a 100 ml hydrothermal reactor and react it at 120℃ for 12 h. After cooling, filter the solution, wash it twice with DMF and once with methanol, and then dry it under vacuum at 80℃ for 12 h. The resulting sample is named CNT / MOF.

[0071] Step 3: Add 0.1g CNT / MOF and 0.03g sodium carboxymethyl cellulose (CMC-Na) dispersant to 40mL deionized water and stir for 1h to obtain solution B.

[0072] Step 4: Dissolve 0.03 g of pore-forming agent NH4HCO3 and 0.03 g of thermal initiator potassium persulfate (KPS) in 40 mL of deionized water for 1 hour.

[0073] Step 5: Add the solution A obtained in step 3, 0.01 g of MBA and 1 g of AAM to the solution and mix thoroughly. Stir for 2 h to obtain a uniformly dispersed emulsion.

[0074] Step 6: Transfer the emulsion obtained in step 5 into a mold and react at 80°C for 2 h to finally obtain CNT / MOF hydrogel.

[0075] The prepared CNT / MOF hydrogel absorbing material has a minimum reflection loss of -20.03 dB and an effective absorption bandwidth of 0.671 GHz. It exhibits a tensile strength of 12.2 MPa and an elongation at break of 710.8%.

[0076] Comparative Example 3 This comparative example provides a MOF composite hydrogel, and the specific process is as follows: Step 1: Dissolve 0.4 mmol of zirconium tetrachloride and 0.4 mmol of 2-aminoterephthalic acid in 40 mL of N,N-dimethylformamide (DMF). After sonication to dissolve, add 8 mL of glacial acetic acid while stirring. Then add 30% of the total mass of CNT and stir for 1 h.

[0077] Step 2: Transfer the solution obtained in Step 1 to a 100 ml hydrothermal reactor and react it at 120℃ for 12 h. After cooling, filter the solution, wash it twice with DMF and once with methanol, and then dry it under vacuum at 80℃ for 12 h. The resulting sample is named CNT / MOF.

[0078] The prepared CNT / MOF absorbing material has a minimum reflection loss of -48.98 dB and an effective absorption bandwidth of 2.302 GHz.

[0079] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that no ionic liquid was added in step 4. The specific step 4 is as follows: Step 4: Dissolve 0.4 mmol of zirconium tetrachloride and 0.4 mmol of 2-aminoterephthalic acid in 40 mL of N,N-dimethylformamide (DMF). After sonication to dissolve, add 8 mL of glacial acetic acid while stirring. Then add 20% of the total mass of PCNT and stir for 1 h.

[0080] The prepared CNT / MOF absorbing material has a minimum reflection loss of -22.31dB and an effective absorption bandwidth of 2.07GHz.

Claims

1. A hydrogel, characterized in that: Zirconium-based MOFs are dispersed in the hydrogel; The zirconium-based MOFs are loaded with carbon nanotubes coated with polydopamine. The organic ligand of the zirconium-based MOFs is 2-aminoterephthalic acid; The zirconium-based MOFs contain unsaturated metal sites.

2. The hydrogel as described in claim 1, characterized in that: Its preparation method includes the following steps: Carbon nanotubes were dispersed in an alkaline Tris-HCl buffer solution, then dopamine salt was added, the reaction was carried out and the mixture was separated to obtain carbon nanotubes coated with polydopamine. Zirconium salt, ionic liquid and 2-aminoterephthalic acid were dissolved in an organic solvent, glacial acetic acid was added to react, and then carbon nanotubes coated with polydopamine were added and subjected to hydrothermal reaction to obtain zirconium-based MOFs loaded with carbon nanotubes coated with polydopamine. Zirconium-based MOFs loaded with carbon nanotubes coated with polydopamine and a dispersant were mixed in water to obtain solution A; The pore-forming agent and initiator are mixed with water to obtain solution B; Solution A, N,N'-methylenebisacrylamide, and acrylamide were added to solution B and mixed to obtain an emulsion, which was then reacted to obtain the final product. The ionic liquid is Where 2≤m≤10, X includes Cl - .

3. The hydrogel as described in claim 2, characterized in that: The pH value of the Tris-HCl buffer solution is 8-9.

4. The hydrogel according to claim 2, characterized in that: The mass ratio of dopamine salt to CNT is 1:2 to 1:

5.

5. The hydrogel according to claim 2, characterized in that: The separation includes centrifugal separation; The centrifugation speed is 8000-10000 r / min.

6. The hydrogel according to claim 2, characterized in that: The organic solvent includes N,N-dimethylformamide; The molar ratio of zirconium salt, ionic liquid and 2-aminoterephthalic acid is 4:0.1-0.3:

4.

7. The hydrogel according to claim 2, characterized in that: The temperature of the hydrothermal reaction is 100-140℃.

8. The hydrogel according to claim 2, characterized in that: The amount of glacial acetic acid added is 12.5-25 mL per 1 mol of zirconium salt; Carbon nanotubes coated with polydopamine account for 20-40% of the total mass.

9. The hydrogel according to claim 2, characterized in that: The content of zirconium-based MOFs loaded with polydopamine-coated carbon nanotubes in solution A is 0.0025 g / mL; The dispersant content in solution A is 0.00075 g / mL; The dispersant is sodium carboxymethyl cellulose.

10. The hydrogel according to claim 2, characterized in that: In solution B, the content of pore-forming agent is 0.00075 g / mL; In solution B, the initiator concentration is 0.00075 g / mL; The pore-forming agent is ammonium bicarbonate; The initiator is potassium persulfate; The emulsion contains 0.00025 g / mL of N,N'-methylenebisacrylamide. The acrylamide content in the emulsion is 0.025 g / mL.

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