Facile synthesis of FeCo layered double oxide/raspberry-like carbon microspheres with hierarchical structure for electromagnetic wave absorption.

Transition metal compositions (Fe, Co and Ni) have always been promising candidates for electromagnetic wave (EMW) absorbers. In this study, the FeCo layered double hydroxide (LDH) supported on raspberry-like carbon spheres (RCs) was synthesized by a simple hydrothermal method and the spontaneous electrostatic self-assembly process. The surface FeCo-LDH is then transformed into FeCo layered double oxide (LDO) with different compositions after calcination treatment (650 °C and 700 °C), forming a typical hierarchical structure. The sample calcined at 700 °C exhibited an ultra-wide effective absorption bandwidth (f) (RL < -10 dB) of 7.4 GHz (from 10.6 to 18.0 GHz) at the matched thickness of 2.2 mm. The remarkable EM wave absorption properties are attributed to the strong interface polarization due to the various phase boundaries in LDO shell as well as sufficient heterointerfaces between LDO shell and RCs. It should be emphasized that LDH is rarely used for EMW absorption, and the use of LDH positively charged characteristics to fabricate hierarchical materials is a meaningful attempt and confirms the potential of LDH in EMW absorbing materials.