Abstract: Metal-organic frameworks (MOFs) derived composites are extremely potential electromagnetic wave (EMW) absorbers. However, the permittivity of absorbers directly derived from MOFs with solid structure is usually relatively low, inevitably limiting their further applications. Cation substitution can primely overcome the problem by regulating the morphology and atomic space occupation to enhance multiple loss mechanisms and impedance matching characteristics. However, universal mechanisms of the effect on EMW absorption performance influenced by cation substitution are still comparatively inadequate, which prospectively requires further exploration. Herein, a series of imidazolic MOFs were fabricated by ultrasonic symbiosis method and tailored by subsequent cation substitution strategy to prepare target porous composites. At a low filling rate and thin thickness, the as-obtained samples reach the optimal reflection loss and effective absorption bandwidth values of -49.81 dB and 7.63 GHz, respectively. The intercoupling between multiple atoms lays a significant foundation for abundant heterogeneous interfaces and defect vacancies, which effectively ameliorate the attenuation mechanisms. Meanwhile, the porous structure introduced by cation substitution reduces the bulk density to enhance the impedance matching and multiple reflections simultaneously. This study provides a helpful idea to exceedingly improve the EMW absorbing performance of imidazolic MOFs-derived composites by cation substitution.

Key words: Multiple attenuation mechanisms, Cation substitution, Porous composites, Electromagnetic wave absorption