Self-assembly synthesis and microwave absorption properties of magnetic functionalized graphene aerogels

Graphene aerogels anchored ultra-fine Fe3O4 nanoparticles with multifunctional electromagnetic and interfacial properties were successfully constructed via chemically self-assembly and in situ pyrolysis. The well-established structure and ultrafine nanoparticles are vital for high-performance microwave absorption materials. The hybrids with only 5% filling contents exhibited excellent microwave absorption performance (MAP) in terms of both minimum reflection loss (RLmin) and effective absorption bandwidth (EAB). outperforming the most reported microwave absorbers. Importantly, experimental results and theoretical calculations indicate that superior MAP can be carried out by reasonably regulating the electromagnetic parameters. Considering the excellent electromagnetic and interfacial properties. our strategy opened a novel way for anchoring ultra-small nanoparticles on graphene sheets as highly effective synergistic microwave absorbers at low filling contents. With the quick development of information technology, electromagnetic pollution originating from extensive use of the associated electronic devices has raised serious concerns, which not only impacts the operation of precision electronic instruments but also threatens public health and people's living environment. The development of high-performance microwave absorption materials (MAMs) is one of the most straightforward ways to eliminate unwanted electromagnetic waves. As a consequence, the rational design and construction of MAMs that are capable of efficiently enhancing microwave absorption capacities are under highly active research. The microwave absorption performances are mainly affected by the relative complex permittivity and permeability, impedance matching, the attenuation characteristics as well as the microstructures. Currently, various MAMs have been reported, including metal powder, metal alloy as well as conductive polymer and different structure composites including hollow structure, core-shell structure and porous structure. Among these, the most promising materials are Fe3O4-based composites, which have also been widely explored as MAMs in electromagnetic shielding and microwave absorption. Recently, carbon-based materials, such as carbon nanotubes (CNTs), carbon foams (CFs), carbon fibers (CNFs), carbon spheres (CSs) and graphene, have drawn considerable research interest. Graphene aerogels (GAs) acting as a new kind of three-dimensional (3D) porous networks have attracted tremendous attention due to their superior characteristics including light weight, high porosity and excellent mechanical, electronic, thermal properties. Yet, many researchers have proved that absorbers with only one single composition are unable to satisfy the requirements of new absorbing materials, which generally pursue thin thickness, light weight, wide absorption range and strong absorption characteristics at low filling content (< 5wt%). Coupling of magnetic loss materials (Fe/Co/Ni/alloys and compounds, etc.) and dielectric loss materials (SiO2/TiO2/graphene, etc.) generates synergistic effects, which are beneficial to microwave absorption performances. Interestingly, graphene aerogels show a high specific surface area. which can be used as carriers to load nanoparticles. They can not only effectively solve the agglomeration of different nanoparticles and the uniform dispersion in the matrix, but also can optimize the structure on the nanoscale. As a consequence, the specific composition, structure, and properties of multifunctional grapheme aerogels composites were prepared. Magnetic nanoparticles (MNPs) have many applications because of excellent magnetic properties. Among them, Fe3O4 MNPs have attracted great attention due to their good biocompatibility, low-cost preparation and low toxicity. The introduction of Fe3O4 functionalized graphene contributes to the high complex permeability and significantly enhances the microwave absorption properties. Based on the self-assembly-lyophilization-pyrolysis techniques, by creatively selecting water-insoluble acetylacetone complex as the iron source, and ascorbic acid as the reducing agent and solubilizer for the first time, the ultralight and super-hydrophobic graphene aerogels decorated with ultra-fine Fe3O4 nanocrystals (HGAFX, X stands for the pyrolysis temperature) were synthesized in an aqueous solvent. Graphene nanosheets function as a protective coating to effectively prevent Fe3O4 nanocrystals from aggregation, while the special porous structure provides numerous channels for reflection and scattering of the electromagnetic wave. Interestingly, the filling volumes have a significant effect on the electromagnetic properties. Therefore, the electromagnetic parameters of magnetic graphene aerogels can be regulated by changing filling volumes and excellent microwave absorption performance can be achieved at a low filling level.