Ultra-broadband microwave absorption of honeycomb-like three-dimensional carbon foams embedded with zero-dimensional magnetic quantum dots

The magnetic response behavior of microwave absorbing materials (MAMs) is beneficial to the expansion of the effective bandwidth in the high-frequency electromagnetic fields. However, the high density of magnetic components does not match with the lightweight requirement of MAMs. In response to this contradiction, the metal-organic framework (MOF) ZIF-67 material and melamine foam were used in the present work as the magnetic component and self-sacrificial template, respectively. A three-dimensional honeycomb carbon foam with zero-dimensional magnetic Co quantum dots (Co-QDs/CF) was prepared by a simple two-step method. The unique honeycomb structure significantly improved impedance matching and carrier mobility , providing more scattering paths for the electromagnetic wave conduction while reducing the overall density. In turn, the uniformly embedded magnetic Co-QDs endowed the 3D carbon foam with excellent high-frequency magnetic response while ensuring light weight. The ultra-small size (<10 nm) enhanced the exchange coupling between magnetic particles while suppressing the eddy current effect, and the magnetic loss capability was greatly improved. Interestingly, Co-QDs acting as numerous micro-resistors formed a large three-dimensional conductive network with the carbon skeleton, which demonstrated outstanding electron transport ability, so that the conductance loss was significantly enhanced. Surprisingly, the effective absorption bandwidth of Co-QDs/CF in the 2–18 GHz band was as high as 8.74 GHz with a matching thickness of 2.5 mm, while the corresponding filling rate was only 20 wt%. Thus, the proposed ingenious strategy to construct three-dimensional conductive networks using ultra-small magnetic quantum dots opens up new prospects for the development of lightweight broadband MAMs.