Fe3+ induced CoFe@hollow carbon nanocage morphology engineering modulation for tunable microwave absorption based on the Kirkendall effect

The precise modulation of morphology engineering utilizing metal-organic frameworks (MOFs) presents a promising avenue for the development of optimal microwave absorbers. Nonetheless, challenges emerge due to the tendency of MOF derivatives to either collapse or exist in isolation, which can impede the dissipation of electromagnetic waves (EMWs) and diminish their efficacy as microwave absorbers. Herein, this work proposes a pragmatic strategy for modulating the dielectric properties of MOF derivatives through the incorporation of Fe. By introducing Fe 3+ into the ZIF-67-on-ZIF-8 precursor, and leveraging the Kirkendall effect, a CoFe@hollow carbon nanocage (HCN) structure with a large opening is synthesized post-pyrolysis. This structure effectively addresses the issues related to the contact between MOF derivatives and their inadequate conductivity, resulting in remarkable microwave absorption (MA) performance at a low paraffin filling ratio of 15 wt%. The amount of Fe doping allows for flexible control over the dielectric properties, which are influenced by morphological evolution and the extent of graphitization, leading to tunable MA characteristics. Consequently, exceptional MA performance is achieved, characterized by both broad bandwidth absorption (6.3 GHz) and high-efficiency loss (-60.09 dB). This research elucidates an intrinsic mechanism linking microtopology to MA properties, offering significant insights that are anticipated to guide the future development of dielectric MA materials through morphology engineering methodologies.