Hollow engineering of carbon-based microspheres: Microstructural modulation for advanced electromagnetic wave absorption

Electromagnetic (EM) absorption is becoming a progressive strategy to address the concerns in the fields of EM pollution, information security, and military stealth. In addition to the composition of EM wave absorbing materials (EWAMs), the design of morphology and microstructure has also been evolved into another core topic for optimizing their performance, because it directly affects their impedance matching, loss mechanism, response bandwidth, and environmental adaptability. As one kind of promising candidates, hollow carbon-based microspheres (HCBMs) have been intensively studied in the past decade, not only for their diverse composition, tunable EM characteristics, and profitable hollow cavity, but also for their uniform size and good dispersion, offering a great opportunity for the fabrication of customized structural-functional integrated materials through additive manufacturing. In this review, we introduce some mature and emerging route for HCBMs, including hard template, post-modification, spray drying, self-assembly, and heterogeneous contraction resistance, and highlight the advances of the resultant HCBMs in EM absorption. Moreover, some challenges and prospects are also proposed from the perspective of current research progress, and we hope this review may inspire further development of HCBMs.