Porous Carbon/ZnO Composites Synthesized Using an Environmentally Friendly Metal-Polyphenol Network for Electromagnetic Wave Absorption

Composite materials made of transition metals/metallic oxides and porous carbon stemming from metal-organic frameworks (MOFs) have drawn tremendous attention within the field of electromagnetic wave absorption. However, the fabrication of most MOFs involves the use of toxic solvents and specially synthesized organic ligands; furthermore, high-pressure hydrothermal processes are commonly employed and are environmentally unfriendly and unsustainable. Herein, a Zn metal-polyphenol network (MPN) was developed by replacing organic ligands with biomass tannic acid at room temperature by using water and ethanol as solvents. The resulting MPN exhibited a microstructure and performance similar to those of MOFs. Subsequently, in situ pyrolysis of the Zn-tannic acid network was conducted to prepare porous carbon/ZnO (PC/ZnO) composites. The PC/ZnO composite pyrolyzed at 700 degree celsius showed a strong reflection loss of -57.8 dB at a matching thickness of 3.5 mm, and a wide effective absorption bandwidth of 5.5 GHz was attained at 2.5 mm. The excellent electromagnetic wave absorption performance can be ascribed to the occurrence of multiple scattering events due to the porous structure, the moderate resistance loss of the porous carbon network, and the strong dipolar and interfacial polarization losses due to the ZnO nanoparticles and defect carbon. This study provides a convenient, environmentally friendly, sustainable, and tunable approach to prepare excellent broadband electromagnetic wave absorbers.