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Professor Hui Zhang & Associate Professor Liying Zhang from Donghua University: Exploring the Structural Evolution Mechanism of ZIF-67 via Electrospinning Strategy to Enhance Electromagnetic Wave Absorption in ZIF-67-Derived Carbon Nanofibers
With the widespread adoption of 5G and smart devices, electromagnetic pollution has become increasingly severe, driving growing demand for research on wave-absorbing materials. Carbon nanofibers (CNFs) are ideal wave-absorbing substrate materials due to their lightweight nature and conductivity, while MOF-derived materials are widely used to enhance wave-absorbing performance owing to their tunable structures and high specific surface area.
Most reported studies on MOF-derived composite wave-absorbing fibers employ non-in-situ electrospinning strategies, where pre-synthesized MOF particles are directly added to the spinning solution for electrospinning.This work adopts an in-situ electrospinning technique, where ZIF-67 structures are grown in-situ on fiber surfaces during the electrospinning process. By comparing the effects of in-situ and non-in-situ methods on the structural evolution of ZIF-67, the study reveals the structural evolution mechanism of ZIF-67 and prepares high-performance ZIF-67-derived carbon nanofibers for electromagnetic wave absorption.
Recently, the research team of Professor Hui Zhang and Associate Professor Liying Zhang at Donghua University published their latest findings in *Advanced Science*: *"Mechanistic Insights into the Structural Evolution of ZIF-67 via Electrospinning Strategy Toward High Electromagnetic Wave Absorption Performance of ZIF-67-Derived Carbon Nanofibers."* The researchers constructed ZIF-67-derived Co/C nanofiber composites using both in-situ and non-in-situ electrospinning strategies, systematically comparing the differences in ZIF-67 structural evolution, Co particle distribution, and electromagnetic wave absorption performance (Figure 1).The results show that the in-situ electrospinning strategy enables uniform generation of small-sized Co nanoparticles on fiber surfaces, forming a continuous conductive network and abundant polarization interfaces. In contrast, samples prepared via the non-in-situ electrospinning strategy contain larger Co particles primarily encapsulated within the carbon matrix. The in-situ samples exhibit superior impedance matching, conductive loss, and magnetic loss, achieving a minimum reflection loss (RLmin) of -48.6 dB at a thickness of 3.5 mm. This study not only elucidates the structural evolution mechanism of ZIF-67 nanoparticles but also provides theoretical and experimental support for the design of high-performance fibrous wave-absorbing materials.
Figure 1.Schematic of the preparation methods for ex-Co-CNF and in-Co-CNF.
As shown in Figure 2, under the in-situ electrospinning strategy, the formed ZIF-67 particles are smaller in size and collapse into small Co nanoparticles after carbonization, uniformly distributed on the fiber surface (in-Co-CNF). In contrast, samples synthesized via the non-in-situ electrospinning strategy contain larger ZIF-67 particles that retain their polyhedral skeleton structure after carbonization and encapsulate large-sized Co particles (ex-Co-CNF). The size differences lead to variations in the spatial distribution of particles within the material, directly affecting its electromagnetic properties. Based on these findings, the study reveals the conversion mechanism of ZIF-67 to Co nanoparticles, clarifies the formation and distribution patterns of Co nanoparticles, and provides theoretical guidance for the structural optimization of MOF-derived electromagnetic wave-absorbing materials.
Figure 2. Sample morphology analysis and schematic of the ZIF-67 to Co nanoparticle evolution mechanism.
As shown in Figure 3, in electromagnetic absorption performance tests, the in-Co-CNF sample achieved an RLmin of -48.6 dB at 6.8 GHz with a thickness of 3.5 mm and an effective absorption bandwidth (EAB) of 4.2 GHz, outperforming the ex-Co-CNF sample (RLmin: -18.3 dB, 9.3 GHz).
Figure 3. Electromagnetic wave absorption performance of the samples.
The electromagnetic wave absorption mechanism diagram (Figure 4) shows that since the Co content in both ex-Co-CNF and in-Co-CNF is nearly identical, the size and distribution of Co nanoparticles play a crucial role in EMW absorption performance. Large-sized Co nanoparticles are located on the ZIF-67-derived carbon skeleton in ex-Co-CNF. The introduction of Co nanoparticles creates heterogeneous interfaces between Co and carbon structures, leading to charge accumulation and promoting interfacial polarization. Additionally, the introduction of Co nanoparticles induces significant magnetic loss. In contrast, the collapse of the ZIF-67 framework in in-Co-CNF results in uniform dispersion of smaller Co nanoparticles within the carbon skeleton network, generating more heterogeneous interfaces and enriching polarization centers, thereby enhancing wave-absorbing performance.
Figure 4.Schematic diagram of EMW absorption mechanisms for ex-Co-CNF and in-Co-CNF.
Simulated radar cross-section (RCS) results demonstrate that the in-Co-CNF sample exhibits excellent stealth performance at multiple angles, with the lowest RCS value reaching -37.3 dB m², far superior to ex-Co-CNF (−8.1 dB m²). Meanwhile, Tesla coil experiments confirm the material's effective electromagnetic wave absorption capability.
Figure 5. RCS results and EMW absorption of in-Co-CNF in Tesla wireless transmission experiments.
In summary, this study constructs carbon nanofiber wave-absorbing materials loaded with Co nanoparticles of different morphologies via in-situ and non-in-situ electrospinning strategies. It not only reveals the structural evolution mechanism of ZIF-67 to Co nanoparticles but also provides new insights for the design and application of high-performance electromagnetic wave-absorbing materials.
Paper link: http://doi.org/10.1002/advs.202502560
