Generation of graphene-based aerogel microspheres for broadband and tunable high-performance microwave absorption by electrospinning-freeze drying process

Despite recent progress in the synthesis and application of graphene-based aerogels, some challenges such as scalable and cost-effective production, and miniaturization still remain, which hinder the practical application of these materials. Here we report a large-scale electrospinning method to generate graphene-based aerogel microspheres (AMs), which show broadband, tunable and high-performance microwave absorption. Graphene/Fe₃O₄ AMs with a large number of openings with hierarchical connecting radial microchannels can be obtained via electrospinning-freeze drying followed by calcination. Importantly, for a given Fe₃O₄: graphene mass ratio, altering the shape of aerogel monoliths or powders into aerogel microspheres leads to unique electromagnetic wave properties. As expected, the reflection loss of graphene/Fe₃O₄ AMs-1:1 with only 5 wt.% absorber loading reaches?51.5 dB at 9.2 GHz with a thickness of 4.0 mm and a broad absorption bandwidth (R_L < -10 dB) of 6.5 GHz. Furthermore, switching to coaxial electrospinning enables the fabrication of SiO₂ coatings to construct graphene/Fe₃O₄@SiO₂ core?shell AMs. The coatings influence the electromagnetic wave absorption of graphene/Fe₃O₄ AMs significantly. In view of these advantages, we believe that this processing technique may be extended to fabricate a wide range of unique graphene-based architectures for functional design and applications.