A zif-derived cobalt monatomic / nanoparticle / aqueous polyurethane composite wave-absorbing and heat-conducting material and a preparation method thereof

Abstract

This invention discloses a ZIF-derived cobalt single-atom / nanoparticle / waterborne polyurethane composite microwave absorbing and thermally conductive material and its preparation method, belonging to the technical field of multifunctional composite materials for electromagnetic protection and thermal management. By controlling the pyrolysis and acid washing of bimetallic ZIF, a heterostructure of cobalt single atoms and cobalt nanoparticles uniformly dispersed in a nitrogen-doped porous carbon network is constructed, and these are introduced into a polymer matrix as a multifunctional filler. The abundant heterostructure interfaces and conductive pathways in this material synergistically enhance dielectric / magnetic loss and impedance matching, achieving efficient microwave absorption. Simultaneously, the continuous carbon framework and the high thermal conductivity metal component form an effective heat conduction path, significantly improving the thermal conductivity of the composite system. The method of this invention is simple and scalable, and the product possesses integrated electromagnetic absorption and heat dissipation functions, demonstrating good application prospects and practical value.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive and microwave-absorbing composite material preparation and electronic packaging technology, specifically relating to a ZIF-derived cobalt single atom / nanoparticle / waterborne polyurethane and its preparation method. Background Technology

[0002] With the rapid development of electronic devices towards higher power, higher frequency, and higher integration, electromagnetic interference and thermal management issues are becoming increasingly prominent. High-frequency circuits not only generate strong electromagnetic radiation during operation, interfering with the stability of communication systems, but also cause significant temperature rises due to energy loss. Traditional designs typically introduce absorbing and thermally conductive layers between the chip and the heat dissipation structure to address electromagnetic compatibility and heat dissipation requirements respectively. However, absorbing materials generally have low thermal conductivity, and their insertion significantly increases interfacial thermal resistance. Simultaneously, the absorbed electromagnetic energy is converted into heat energy; if it cannot be dissipated in time, it will lead to localized overheating, which in turn weakens the dielectric or magnetic loss properties of the material, creating a vicious cycle of mutual constraint between absorption and heat dissipation. Therefore, developing integrated dual-functional materials that combine efficient microwave absorption and high thermal conductivity has become a key requirement for advanced electronic packaging.

[0003] In recent years, porous carbon composites derived from metal-organic frameworks (MOFs) have shown great potential in broadband microwave absorption due to their tunable electromagnetic parameters and abundant polarization interfaces. In particular, systems containing transition metals can enhance absorption intensity through the synergistic effect of magnetic and dielectric losses. By precisely controlling pyrolysis conditions, high-density single-atom metal particles can be stably anchored within a carbon matrix. These atomically dispersed active centers not only effectively improve magnetic loss capability and avoid eddy current losses caused by the excessive size of traditional nanoparticles, but also serve as low-scattering nodes for phonon transport, contributing to improved overall heat conduction pathways.

[0004] To improve thermal transport properties, flexible polymer matrices are often used as the continuous phase in composite materials due to their good processability, elasticity, and interfacial adaptability, which can effectively fill microscopic voids and reduce contact thermal resistance. However, the disordered arrangement of polymer molecular chains leads to strong phonon scattering, and the intrinsic thermal conductivity is typically below 0.3 W·m. -1 ·K -1 Although a heat conduction network can be constructed to some extent by introducing high thermal conductivity fillers, how to improve thermal conductivity while avoiding enhanced electromagnetic reflection or impedance mismatch remains a major challenge for achieving efficient electromagnetic-thermal synergistic management. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient dual-function ZIF-derived cobalt single-atom / nanoparticle / waterborne polyurethane with electromagnetic wave absorption and thermal conductivity, and its preparation method, in order to solve the problems of electromagnetic interference and heat accumulation in the operation of electronic devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: First, ZIF-67-m / ZIF-8-n with different metal ratios were synthesized via a one-pot method. Then, after calcination and acid washing, ZIF derivatives were obtained. These ZIF derivatives were then added to waterborne polyurethane and cured to finally obtain the composite material. The process includes the following steps: (1) Weigh 200 parts of methanol by mass and divide it into two equal parts. Dissolve cobalt acetate and zinc acetate in different proportions in 100 parts of methanol and mix them evenly. Add another 100 parts of methanol solution containing a certain amount of 2-methylimidazole while stirring continuously. React at 15-30℃ for 12-24 h, centrifuge, wash with methanol, and activate under vacuum at 60℃ for 3-5 h to obtain ZIF-67-m / ZIF-8-n, where m and n are the mmol of cobalt acetate and zinc acetate, respectively. (2) ZIF-67-m / ZIF-8-n was heated to 1000-1200℃ in Ar atmosphere at a heating rate of 5℃ / min, calcined for 1-2 h, ground, acid-washed at 60-80℃ for 12-24 h, filtered, and vacuum activated at 60℃ for 1-2 h to obtain ZIF derivative Co-N / Co / C-mn; (3) Add waterborne polyurethane to ZIF derivative, mix evenly, and polymerize at 15-30℃ for 24 h to obtain the ZIF-derived cobalt single atom / nanoparticle / waterborne polyurethane composite material Co-N / Co / C-mn-WPU.

[0007] Further, in step (1), the molar ratio of zinc acetate to cobalt acetate is 1-100:100, the total amount of zinc acetate and cobalt acetate is 25-40:100 to 2-methylimidazole, the pickling solution in step (2) is sulfuric acid, and the mass ratio of waterborne polyurethane to ZIF derivative in step (3) is 10-20:100.

[0008] The ZIF-derived cobalt single-atom / nanoparticle / waterborne polyurethane composite material prepared in this invention uses a heterostructure obtained from the controlled pyrolysis of bimetallic ZIF, in which cobalt single atoms and cobalt nanoparticles are uniformly dispersed in a nitrogen-doped porous carbon network, as a multifunctional filler introduced into a waterborne polyurethane matrix. This heterostructure not only constructs abundant interfacial polarization centers and continuous conductive pathways, synergistically enhancing dielectric and magnetic loss capabilities and optimizing impedance matching to achieve efficient microwave absorption; simultaneously, the nitrogen-doped carbon framework and the highly thermally conductive cobalt component together form an effective three-dimensional thermal conduction network, significantly improving the thermal conductivity of the composite material and mitigating heat accumulation caused by electromagnetic losses. This invention proposes a novel method for developing multifunctional materials that combine microwave absorption and thermal conductivity.

[0009] The beneficial effects of this invention are as follows: (1) A bimetallic ZIF precursor was synthesized at room temperature and Zn was selectively evaporated by high-temperature pyrolysis. A nitrogen-doped carbon framework with high specific surface area and multi-level channels was constructed in situ, which is beneficial for electromagnetic wave multiple scattering and penetration.

[0010] (2) By controlling the pyrolysis and acid washing conditions, cobalt single atoms and cobalt nanoparticles coexist in a carbon matrix, forming rich heterogeneous interfaces and magnetoelectric synergistic effects, significantly improving dielectric / magnetic loss capability and optimizing impedance matching. Based on the pore-forming effect of Zn volatilization, this invention further introduces an acid washing step. This step not only effectively removes residual Zn but also specifically dissolves free Co particles exposed on the carbon framework surface, thus retaining two key active components: atomically dispersed Co single atoms and Co metal nanoparticles tightly coated by a carbon layer. Co single atoms provide abundant coordination unsaturated sites and local dipoles, significantly enhancing the polarization relaxation loss of the material; while the carbon coating structure acts as a dielectric buffer layer, effectively controlling the complex dielectric constant of the composite material and avoiding impedance mismatch problems caused by an excessively strong conductive network. This unique microstructure achieves a fine synergy between dielectric and magnetic losses, greatly improving the overall impedance matching performance.

[0011] (3) This invention specifically selects waterborne polyurethane as the matrix, which is not only more environmentally friendly, but the prepared composite material also exhibits excellent electromagnetic wave absorption performance and good thermal conductivity. This thermal conductivity stems from the unique porous carbon skeleton structure of this invention and the highly efficient thermally conductive network constructed by Co single atoms / carbon-coated Co particles. In practical applications of electronic devices, this characteristic means that the material can not only effectively suppress electromagnetic interference, but also simultaneously alleviate the heat accumulation problem generated during equipment operation, realizing the integration of wave absorption and heat conduction, and has significant application advantages and innovative value.

[0012] (4) The continuous nitrogen-doped carbon network and the high thermal conductivity cobalt component in the composite material form an efficient thermal conduction path, which achieves excellent microwave absorption performance while having good thermal conductivity. Attached Figure Description

[0013] Figure 1 The images are (a) XRD pattern, (b) HAADF-STEM image, (c) Co K-edge XANES pattern, and (d) R-space EXAFS pattern of Co-N / Co / C-mn of the present invention.

[0014] Figure 2 The complex permittivity of the Co-N / Co / C-mn-WPU of this invention is represented by (a) the real part, (b) the imaginary part, and (c) the dielectric loss tangent tanδ. ε .

[0015] Figure 3The (a) conduction loss ε of the Co-N / Co / C-mn-WPU of this invention is c "and polarization loss ε" p (b) Minimum reflection loss RL min Curve, (c) Impedance matching coefficient |Z under minimum reflection loss in / Z0| and the attenuation constant α.

[0016] Figure 4 This is a comparison of the microwave absorption performance of the Co-N / Co / C-28-WPU and the un-acid-washed sample of the present invention.

[0017] Figure 5 The microwave energy storage efficiency w of the Co-N / Co / C-mn-WPU of this invention is (a) s (b) Electromagnetic wave energy conversion efficiency w d (c) Through conduction loss w c and (d) polarization loss w p Efficiency of energy conversion.

[0018] Figure 6 The thermal conductivity of the Co-N / Co / C-mn-WPU and WPU of this invention is [not specified]. Detailed Implementation

[0019] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention. Example 1

[0020] 2 mmol cobalt acetate and 8 mmol zinc acetate were dissolved in 100 mL methanol. 100 mL of a methanol solution containing 30 mmol 2-methylimidazole was added with continuous stirring. The mixture was stirred continuously at room temperature for approximately 12 h. The precipitate was then collected by centrifugation at 9000 rpm for 5 min, washed twice with methanol, and activated at 60 °C for 6 h. The obtained material was labeled ZIF-67-2 / ZIF-8-8. The ZIF-67-2 / ZIF-8-8 sample was ground and then activated at 5 °C·min under an Ar atmosphere. -1The temperature was increased to 1200℃ and held for 1 hour. Afterwards, the sample was naturally cooled to room temperature, collected, ground, and then immersed in a 4 mol / L sulfuric acid solution. It was then ultrasonically dispersed for 10 minutes and acid-washed in an oil bath at 80℃ for 12 hours. The black solid was separated by filtration and washed twice with ethanol. The final product, obtained by drying at 60℃ for 1 hour, was labeled Co-N / Co / C-28. Co-N / Co / C-28 was mixed with waterborne polyurethane (WPU) at a mass fraction of 12.5 wt.%, and the mixed sample was placed in a 20×20×5 mm immersion tank. 3 The Co-N / Co / C-28-WPU composite material was obtained by curing it in a mold at 25°C for 24 hours. Example 2

[0021] 5 mmol cobalt acetate and 5 mmol zinc acetate were dissolved in 100 mL of methanol. 100 mL of a methanol solution containing 30 mmol 2-methylimidazole was added with continuous stirring. The mixture was stirred continuously at room temperature for approximately 12 h. The precipitate was then collected by centrifugation at 9000 rpm for 5 min, washed twice with methanol, and activated at 60 °C for 6 h. The obtained material was labeled ZIF-67-5 / ZIF-8-5. The ZIF-67-5 / ZIF-8-5 sample was ground and then activated at 5 °C·min under an Ar atmosphere. -1 The temperature was increased to 1200℃ and held for 1 hour. Afterwards, the sample was naturally cooled to room temperature, collected, ground, and then immersed in a 4 mol / L sulfuric acid solution. It was then ultrasonically dispersed for 10 minutes and acid-washed in an oil bath at 80℃ for 12 hours. The black solid was separated by filtration and washed twice with ethanol. The final product, obtained by drying at 60℃ for 1 hour, was labeled Co-N / Co / C-55. Co-N / Co / C-55 was mixed with waterborne polyurethane (WPU) at a mass fraction of 12.5 wt.%, and the mixed sample was placed in a 20×20×5 mm immersion tank. 3 The Co-N / Co / C-55-WPU composite material was obtained by curing it in a mold at 25°C for 24 hours. Example 3

[0022] 8 mmol cobalt acetate and 2 mmol zinc acetate were dissolved in 100 mL methanol. 100 mL of a methanol solution containing 30 mmol 2-methylimidazole was added with continuous stirring. The mixture was stirred continuously at room temperature for approximately 12 h. The precipitate was then collected by centrifugation at 9000 rpm for 5 min, washed twice with methanol, and activated at 60 °C for 6 h. The obtained material was labeled ZIF-67-8 / ZIF-8-2. The ZIF-67-8 / ZIF-8-2 sample was ground and then activated at 5 °C·min under an Ar atmosphere. -1The sample was heated to 1200℃ at a controlled heating rate and held for 1 hour. It was then allowed to cool naturally to room temperature. The sample was collected, ground, and then immersed in a 4 mol / L sulfuric acid solution. It was then ultrasonically dispersed for 10 minutes and acid-washed in an oil bath at 80℃ for 12 hours. The black solid was separated by filtration and washed twice with ethanol. The final product, obtained by drying at 60℃ for 1 hour, was labeled Co-N / Co / C-82. Co-N / Co / C-82 was mixed with waterborne polyurethane (WPU) at a mass fraction of 12.5 wt.%, and the mixed sample was placed in a 20×20×5 mm immersion tank. 3 The Co-N / Co / C-82-WPU composite material was obtained by curing it at 25°C for 24 hours in a mold.

[0023] Comparative Example 1

[0024] 2 mmol cobalt acetate and 8 mmol zinc acetate were dissolved in 100 mL methanol. 100 mL of a methanol solution containing 30 mmol 2-methylimidazole was added with continuous stirring. The mixture was stirred continuously at room temperature for approximately 12 h. The precipitate was then collected by centrifugation at 9000 rpm for 5 min, washed twice with methanol, and activated at 60 °C for 6 h. The obtained material was labeled ZIF-67-2 / ZIF-8-8. The ZIF-67-2 / ZIF-8-8 sample was ground and then activated at 5 °C·min under an Ar atmosphere. -1 The temperature was increased to 1200℃ and held for 1 hour. The sample was then allowed to cool naturally to room temperature, collected, and ground. The final product was labeled Co / CoO-28. Co / CoO-28 was mixed with waterborne polyurethane (WPU) at a mass fraction of 12.5 wt.%, and the mixed sample was placed in a 20×20×5 mm immersion chamber. 3 The Co / CoO-28-WPU composite material was obtained by curing it at 25°C for 24 hours in a mold.

[0025] Figure 1 The structure of Co-N / Co / C-mn is shown, in which the Co species exist as Co single atoms and Co metal particles.

[0026] Figure 2 The dielectric loss capability of Co-N / Co / C-mn-WPU was demonstrated, with Co-N / Co / C-28-WPU exhibiting the strongest dielectric loss.

[0027] Figure 3The study demonstrates that the Co-N / Co / C-28-WPU exhibits the strongest polarization loss and a minimum reflection loss of -64.0 dB at a frequency of 14.4 GHz with a thickness of 2.3 mm, and a maximum effective absorption bandwidth of 5.6 GHz, indicating that the Co-N / Co / C-28-WPU possesses excellent microwave absorption performance. The Co-N / Co / C-28-WPU also exhibits good impedance matching and microwave attenuation capabilities at appropriate frequencies, which are important conditions for its excellent microwave absorption performance.

[0028] Table 1 Co-N / Co / C-28-WPU, Co-N / Co / C-55-WPU, Co-N / Co / C-82-WPU

[0029] As can be seen from Table 1, the Co-N / Co / C-28-WPU obtained by this invention has excellent microwave absorption performance.

[0030] Figure 4 The performance comparison between Co-N / Co / C-28-WPU and the un-acid-washed sample Co / CoO-28-WPU is shown, demonstrating that acid washing plays a significant role in microwave absorption performance.

[0031] Figure 5 The microwave energy storage efficiency of the Co-N / Co / C-28-WPU was demonstrated. w s With a conversion efficiency of over 80%, it exhibits optimal energy conversion capability. This indicates that the Co-N / Co / C-28-WPU can store or convert incident microwave energy into heat energy.

[0032] Figure 6 The thermal conductivity of Co-N / Co / C-mn-WPU and WPU was shown, demonstrating that Co-N / Co / C-28-WPU has excellent thermal management performance.

[0033] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a ZIF-derived cobalt single-atom / nanoparticle / waterborne polyurethane composite microwave absorbing and thermally conductive material, characterized in that: The method comprises the following steps: (1) 200 parts of methanol by mass fraction are divided into two equal parts, and different proportions of cobalt acetate and zinc acetate are dissolved in 100 parts of methanol to mix uniformly, and then another 100 parts of methanol solution containing a certain amount of 2-methylimidazole is added under continuous stirring; the reaction is carried out at 15-30℃ for 12-24 h, centrifuged, washed with methanol, and activated at 60℃ for 3-5 h to obtain ZIF-67 / ZIF-8; (2) The ZIF-67 / ZIF-8 is heated to 1000-1200℃ at a heating rate of 5℃ / min under Ar atmosphere, calcined for 1-2 h, ground, acid washed at 60-80℃ for 12-24 h, filtered, and activated at 60℃ for 1-2 h to obtain a ZIF derivative; (3) The aqueous polyurethane is added to the ZIF derivative and mixed uniformly, and then polymerized at 15-30℃ for 24 h to obtain the ZIF-derived cobalt monatomic / nanoparticle / aqueous polyurethane composite wave-absorbing and heat-conducting material.

2. The method of claim 1, wherein: The molar ratio of zinc acetate to cobalt acetate in step (1) is 1-100:

100.

3. The method of claim 1, wherein: The molar ratio of the total amount of zinc acetate and cobalt acetate to 2-methylimidazole in step (1) is 25-40:

100.

4. The method of claim 1, wherein: The acid washing solution in step (2) is sulfuric acid.

5. The method of claim 1, wherein: The mass ratio of aqueous polyurethane to ZIF derivative in step (3) is 10-20:

100.

6. A ZIF-derived cobalt monatomic / nanoparticle / aqueous polyurethane composite wave-absorbing and heat-conducting material prepared by the method of any one of claims 1-5.

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