Ultrathin MoS2 Nanosheets Encapsulated in Hollow Carbon Spheres: A Case of a Dielectric Absorber with Optimized Impedance for Efficient Microwave Absorption

A dielectric loss-type electromagnetic wave (EMW) absorber, especially over a broad frequency range, is important yet challenging. As the most typical dielectric attenuation absorber, carbon-based nanostructures were highly pursued and studied. However, their poor impedance-matching issues still exist. Here, to further optimize dielectric properties and enhance reflection loss, ultrathin MoS2 nanosheets encapsulated in hollow carbon spheres (MoS2@HCS) were prepared via a facile template method. The diameter and shell thickness of the as-prepared HCSs were similar to 250 and similar to 20 nm. The encapsulated MoS2 nanosheets presented high dispersity and crystallinity. Compared to a pure HCS or MoS2 absorber, MoS2@HCS exhibited an optimized impedance characteristic, which can be attributed to the synergistic effects between HCSs (ensuring rapid electron transmission and compensating the low conductivity of MoS2) and MoS2 nanosheets (exposing sufficient numbers of active sites for polarizations and multi-reflection). Consequently, the MoS2@HCS was endowed with -65 dB EMW attenuation ability under 2 mm and the effective attenuation bandwidth under -20 dB was similar to 3.3 GHz over the K-band under 1.2 mm and similar to 3.4 GHz over the Ka-band under merely 0.7 mm. These results suggested that the MoS2@HCS is a promising dielectric absorber for practical applications. Meanwhile, this work introduces a facile and versatile strategy, which could in principle be extended to other transition metal sulfide@HCS for designing novel EMW absorbers.