Electrospinning Device for Nanofibers| Synthesis of PAN/ZIF-67 derived composite fibers through electrospinningtechnology with superior Ku-band electromagnetic absorption performance

With the rapid development of 5G communication technology, electromagnetic pollution has become a serious problem that needs to be solved urgently. Composite nanofibers prepared by electrospinning, with advantages of low density, high flexibility, and easy processing, have emerged as promising electromagnetic wave (EMW) absorbing materials.This study utilized electrospinning technology to uniformly incorporate cubic-shaped zeolitic imidazolate framework-67 (ZIF-67) into polyacrylonitrile (PAN) fibers, followed by calcination at different temperatures to prepare carbon nanofiber/cobalt oxide/cobalt/nitrogen-doped carbon (CNFs/CoO/Co/NC) composite fibers. The cubic ZIF-67 served as building blocks to construct magnetic carbon composites, forming bamboo-like composite fiber structures with CNFs.The unique microstructure and rational selection of calcination temperature created channels for energy and charge transport, significantly enhancing multiple scattering effects of EMW within the composite fibers. Through precise control of calcination temperature and optimization of impedance matching, the EMW absorption performance of CNFs/CoO/Co/NC composite fibers was remarkably improved, while potential electromagnetic loss mechanisms were proposed.

Recently, Professor Ruiwen Shu's team at Anhui University of Science and Technology published their latest research "Synthesis of PAN/ZIF-67 derived composite fibers through electrospinning technology with superior Ku-band electromagnetic absorption performance" in the journal Carbon. The team successfully prepared CNFs/CoO/Co/NC composite fibers through room-temperature stirring, electrospinning, and subsequent calcination processes.Benefiting from the synergistic effects of unique microstructure and appropriate calcination temperature, these composite fibers exhibited multiple loss mechanisms and excellent impedance matching characteristics. By precisely controlling calcination temperature and optimizing impedance matching, the EMW absorption performance of CNFs/CoO/Co/NC composite fibers was significantly enhanced, providing a new approach for developing high-performance carbon-based EMW absorbing materials.

Figure 1: Schematic diagram of preparation process for CNFs/CoO/Co/NC composite fibers

Figure 1 shows the schematic preparation process of CNFs/CoO/Co/NC composite fibers. First, cubic ZIF-67 was synthesized by room-temperature stirring through coordination self-assembly of cobalt ions (Co2+) and 2-methylimidazole (2-MIM). Then, PAN/ZIF-67 composite fibers were prepared by electrospinning. Finally, calcination transformed PAN/ZIF-67 into CNFs/CoO/Co/NC composite fibers: PAN carbonized into CNFs, Co2+ in ZIF-67 was reduced to metallic Co and partially oxidized to CoO, while nitrogen atoms from decomposed 2-MIM ligands were doped into the carbon skeleton to form NC.

Figure 2: SEM images of sample S2 (a)-(b); TEM images (c); HRTEM images (d)-(e); SAED patterns (f)-(g); Dark-field image (h); Corresponding EDS maps: C (i), N (j), O (k) and Co (l)

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure of S2. As shown in Figures 2(a)-(c), cubic carbon skeletons were effectively integrated into CNFs, forming bamboo-like composite fibers. High-resolution TEM (HRTEM) images in Figures 2(d)-(e) clearly showed lattice fringes corresponding to the (111) plane of CoO (d = 0.245 nm) and the (111) plane of metallic Co (d = 0.209 nm). Selected area electron diffraction (SAED) patterns in Figures 2(f)-(g) further confirmed the coexistence of CoO and Co. EDS mapping showed uniform distribution of C, N, O and Co elements within S2, with Co uniformly distributed in the carbon skeleton.

Figure 3: 3D reflection loss plots and 2D contour maps of samples at 10 wt.% filling rate: S1 (a)-(b), S2 (c)-(d), S3 (e)-(f); Maximum EAB of S2 in the range of 2.6 to 3.8 mm (g); Histogram of RLmin of S2 versus d (h); Radar chart comparison of absorption performance between S2 and other similar composite fibers (i)

As shown in Figure 3, at a low filling rate of 10 wt.% and matching thickness (d) of 3.2 mm, sample S2 exhibited obvious dual-band (partial X-band and entire Ku-band) EMW absorption characteristics, achieving a maximum effective absorption bandwidth (EAB) of 7.92 GHz in the 10.08-18 GHz frequency range. When d was 2.56 mm, the minimum reflection loss (RLmin) reached -63.71 dB. These results demonstrated that precise control of calcination temperature and optimization of impedance matching significantly improved the EMW absorption performance of CNFs/CoO/Co/NC composite fibers.

Figure 4: RCS simulation curves (a); Far-field simulation results of PEC model and models covered with S1, S2 and S3 on PEC (b)-(e); RCS values of PEC model and models covered with S1, S2 and S3 on PEC in the range of -180° to 180° (f)-(i)

Computer simulation technology (CST) was used to simulate the radar cross-section (RCS) values of composite fibers calcined at three different temperatures, verifying their EMW absorption performance. As shown in Figure 4, CNFs/CoO/Co/NC composite fibers (S2) covering a perfect electric conductor (PEC) showed the weakest scattering signal and lowest RCS value (-52.37 dB·m2), indicating the strongest radar scattering dissipation capability. The excellent RCS performance of S2 demonstrated its great potential for practical applications.

Figure 5: Schematic diagram of EMW absorption mechanism of CNFs/CoO/Co/NC composite fibers

In summary, this study prepared PAN/ZIF-67-derived CNFs/CoO/Co/NC composite fibers through room-temperature stirring, electrospinning and subsequent calcination, which exhibited "thin, light, wide and strong" EMW absorption characteristics. Due to their unique microstructure and appropriate calcination temperature, the composite fibers showed multiple dissipation mechanisms and good impedance matching. The intertwined and entangled fiber structure promoted charge and energy transfer, enhancing multiple scattering of incident waves. Moreover, component synergy and construction of abundant heterogeneous interfaces significantly improved the electromagnetic dissipation capability of the composite fibers.Combining experiments, theory and simulations, this study revealed the attenuation and loss mechanisms of EMW by the composite fibers. Therefore, this work provides new insights for preparing PAN-based composite fibers via electrospinning as lightweight, high-efficiency and broadband EMW absorbers.

Paper link: https://doi.org/10.1016/j.carbon.2025.120531