Multilayer hollow Cu/Ni@NC@Cu2-xS nano-boxes with superior low frequency microwave absorption properties

Abstract

Multi-layer hollow Cu/Ni@NC@Cu_2-xS (CNS) nano-boxes were designed using an in situ layered assembly technology, where the surface sulfidation and selective etching of Cu₂O play a key role in the design of hollow structures. Then, adjusting the calcination temperatures can effectively change the degree of the graphitization and form diverse electromagnetic properties. Typically, at 600 °C, CNS nano-boxes exhibit a minimum reflection loss (RL_min) of −50.03 dB and an effective absorption bandwidth (EAB) of 5.68 GHz at 2.81 mm, essentially covering the X-band. Further, a superior low-frequency microwave absorption was gained at 700 °C, where RL_min of −65.78 [email protected] GHz and EAB of 3.84 [email protected] mm are obtained. Impressively, changing the proportion of dopamine (DA) in the raw materials at the calcination temperature of 700 °C, the as-synthesized samples CNS-700-1 and CNS-700-3 also exhibit low RL_min values of −63.37 [email protected] GHz and −44.85 [email protected] GHz, respectively. The in-situ self-polymerization of DA on the surface of Cu_2-xS successfully constructed a multi-layer interface and provided adsorption sites for Ni²⁺ ions. Finally, through pyrolysis, Ni²⁺ ions were reduced to magnetic Ni nanoparticles, achieving the integration of magnetic and electrical components in the material. The CNS nano-boxes possess a unique multi-layer hollow structure and magnetoelectric coupling properties, which effectively regulate the impedance matching, induce the generation of multiple polarizations, and provide excellent low-frequency response characteristics. CST simulation verifies the actual application potential of the composites in specific absorption bands. This work offers a new perspective for the development of low-frequency microwave absorbing materials.