Synthesis and microwave absorption performance of layered hard carbon embedded with ZnO nanoparticles

Abstract

C-based microwave absorbers have attracted intensity research interesting for more than 80 years, and many of them appear to be strong candidates as advanced high-performance microwave absorbers. Hard carbon (HC) based composites, as an important type of C-based materials, however, have rarely been studied as microwave absorbers, and their microwave absorption properties are largely unknown still now. In this study, the composites composed of layered HC embedded with ZnO nanoparticles (LHC@ZnONP) are synthesized by pyrolyzing the mixture of phenolic resin and ZnO nanoparticles.The morphology and structure of the LHC@ZnONP composites are examined by scanning electron microscopy, x-ray diffractometer, Raman spectrometer, transmission electron microscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectrometer. The microwave absorption properties of the as-synthesized composites are characterized by a vector network analyzer in the frequency range of 2–18 GHz. The LHC@ZnONP composites are stacked by HC layers with thickness of ~100 nm and ZnO nanoparticles with diameters of 25 nm, and exhibit a low optimal reflection loss of −38 dB and broad effective absorption bandwidth of 5.7 GHz at an absorption thickness of 3.3 mm. Their high dielectric loss capacity is mainly attributed to the interfacial polarization from the ZnO/HC and LHC/LHC interfaces, as well as the enhanced dipolar polarization caused by the defects, nanopores, and residual organic functional groups in the HC layers. Our study for the first time confirms the excellent microwave absorption properties of HC-based composites, which may provide a new insight for the design of high-performance microwave absorbers.