MOF-on-MOF-Derived CeO₂/Fe@C Composites for Tunable Low-Frequency Electromagnetic Wave Absorption

The rational design of electromagnetic wave (EMW) absorbing materials within the low-frequency range of 2-8 GHz has significant importance. However, achieving controlled low-frequency migration of electromagnetic materials absorption windows remains challenging. In this study, a MOF-on-MOF precursor (UiO-66@MIL-88B) is constructed via an in situ growth strategy and converted into CeO₂/Fe@C (CFC) composites by temperature-programmed pyrolysis, enabling the shift of the absorption window toward lower frequencies. The optimized CFC-2 exhibits excellent low-frequency EMW absorption performance: the minimum reflection loss (RL_min) is -62.20 dB at 7.84 GHz, and the effective absorption bandwidth (EAB) is 5.36 GHz at an ultrathin thickness of 1.70 mm. Notably, increasing the pyrolysis temperature enhances CeO₂ crystallinity and shifts the optimal absorption to lower frequencies, where CFC-3 achieves -42.54 dB at 4.00 GHz. In contrast, Fe@C and CeO₂@C show markedly inferior low-frequency performance. Systematic investigation reveals that the CFC composites with abundant interfaces (Fe/CeO₂, CeO₂/C, and Fe/C), defect-rich carbon, and oxygen vacancies. Multi-scale interfacial polarization, coupled with magnetic loss from Fe nanoparticles, balances dielectric/magnetic losses, improves impedance matching, and enhances attenuation. This work provides a novel strategy for low-frequency EMW absorbers by integrating MOF-on-MOF-derived architectures with temperature-programmed regulation.