Core-shell Fe3O4@CQDs modified by carbon quantum dots: Construction of ultra-broadband and high-efficiency electromagnetic wave absorbers via magnetic-dielectric synergy

Core-shell Fe 3 O 4 @CQDs composites were fabricated via a facile hydrothermal method, and their microstructure as well as electromagnetic parameters were precisely optimized by adjusting CQD loading content. • The distinctive core-shell heterogeneous structure creates abundant interfacial defects and polarization sites. The synergism of dipole polarization, interfacial polarization, multiple scattering and magnetic loss builds multi-channel electromagnetic energy dissipation system. • The as-prepared material exhibits excellent microwave absorption performance with a minimum reflection loss of −77.32 dB and a maximum effective absorption bandwidth of 9.52 GHz, combining strong absorption, broad bandwidth and thin matching thickness. • This work clarifies the structure-performance relationship among component composition, interfacial microstructure and microwave absorption properties. It also broadens the application scope of carbon quantum dots and provides new insights for the design and utilization of carbon-magnetic composite absorbers. The rapid development of modern communication technologies aggravates electromagnetic pollution, creating an urgent need for high-performance electromagnetic wave (EMW) absorbers. Carbon materials are promising candidates due to their tunable microstructures and large specific surface areas. Nevertheless, traditional carbon materials suffer from severe agglomeration and high permittivity, leading to poor impedance matching and narrow effective absorption bandwidth. As an emerging carbon nanomaterial, carbon quantum dots (CQDs) possess low dielectric permittivity, tunable electromagnetic parameters, abundant surface functional groups, ultralow density, good dispersibility and high interfacial activity, while their potential for microwave absorption is still underexplored. Herein, core-shell Fe 3 O 4 @CQDs composites were fabricated via a facile hydrothermal method to overcome the limitations of traditional absorbers including narrow bandwidth, unsatisfactory impedance matching and single loss mechanism. CQDs act as dielectric components and Fe 3 O 4 serves as magnetic loss substrate. Adjusting CQD loading optimizes the microstructure and electromagnetic properties, and the distinctive core-shell heterogeneous structure achieves efficient magneto-dielectric synergistic loss. The optimized Fe 3 O 4 @CQDs-2 shows a minimum reflection loss of −77.32 dB at 2.37 mm and a maximum effective absorption bandwidth of 9.52 GHz, covering the frequency range from 8.48 to 18.00 GHz at a thickness of 3.1 mm. CST simulations confirm its excellent radar stealth performance. This work provides a facile route to prepare lightweight, ultrathin, broadband and high-efficiency EMW absorbers and expands the application of CQDs in electromagnetic functional devices. Download: Download high-res image (146KB) Download: Download full-size image