A novel MOF derivation method is used to prepare Fe/C nanocubes, which are constructed by a cubic framework of amorphous carbon decorated uniformly by Fe@graphitic carbon nanoparticles for microwave absorption.

Highly uniform core-shell composites, polypyrrole@polyaniline (PPy@PANI), have been successfully constructed by directing the polymerization of aniline on the surface of PPy microspheres. The thickness of PANI shells, from 30 to 120 nm, can be well controlled by modulating the weight ratio of aniline and PPy microspheres. PPy microspheres with abundant carbonyl groups have very strong affinity to the conjugated chains of PANI, which is responsible for the spontaneous formation of uniform core-shell microstructures. However, the strong affinity between PPy microspheres and PANI shells does not promote the diffusion or reassembly of two kinds of conjugated chains. Coating PPy microspheres with PANI shells increases the complex permittivity and creates the mechanism of interfacial polarization, where the latter plays an important role in increasing the dielectric loss of PPy@PANI composites. With a proper thickness of PANI shells, the moderate dielectric loss will produce well matched characteristic impedance, so that the microwave absorption properties of these composites can be greatly enhanced. Although PPy@PANI composites herein consume the incident electromagnetic wave by absolute dielectric loss, their performances are still superior or comparable to most PANI-based composites ever reported, indicating that they can be taken as a new kind of promising lightweight microwave absorbers. More importantly, microwave absorption of PPy@PANI composites can be simply modulated not only by the thickness of the absorbers, but also the shell thickness to satisfy the applications in different frequency bands.

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EM pollution, because they can convert the EM energy into thermal energy or dissipate the EM waves through interference. [ 4,5 ] Among many kinds of microwave absorbers, carbon materials are always the most attractive candidates due to their tunable properties, relative low density, abundant resource, easy preparation, and low cost. Various carbon materials, e.g., carbon nanotubes (CNTs), carbon nanofi bers (CNF), carbon nanocoils, and mesoporous carbon, have been utilized to construct highly effective microwave absorbers in the past decades. [6][7][8][9][10][11][12] Although these carbon-based materials have made signifi cant progress in the fi eld of microwave absorption, some elaborate innovations on structure and components are still paving the way for exciting performance to satisfy the requirements of practical applications.Recently, graphene appeared as a fascinating material and grabbed worldwide attention, whose unprecedented physical and chemical properties derived from its unique 2D structure have promised great potential in many research fi elds. [ 13 ] Notably, high charge carrier mobility, extraordinary electrical and thermal conductivity also rendered graphene as a new microwave absorber, and it was found that reduced graphene oxide (rGO) provided superior microwave absorption to graphene oxide (GO). [ 14,15 ] However, sole graphene material suffers from limited loss mechanism caused by interfacial impedance mismatching, [ 15,16 ] thus it is usually employed as EM interference shielding material rather than EM absorbing material. [17][18][19] Incorporation of other lossy materials, especially magnetic metal and metal oxides, has been widely studied as the imperative solution to improve the matching of characteristic impedance and enhance the microwave absorption performance. [20][21][22][23][24][25][26][27][28][29] For example, graphene-coated Fe nanocomposites and Ni/graphene composites showed enhanced microwave absorption due to the charge transfer at metal/graphene interface and the polarization of free carriers; [ 20,21 ] Fe 3 O 4 /graphene, rGO-Fe 2 O 3 , and rGO/CNT-Fe 3 O 4 materials demonstrated optimum characteristic impedance and compatible dielectric and magnetic loss, which resulted in their strong refl ection loss in the frequency range of 12.0-16.0 GHz; [21][22][23] Graphene decorated with coreshell Fe@Fe 3 O 4 @ZnO nanoparticles was also fabricated, and Graphene-based composites offer immense potential for overcoming the challenges related to the performance, functionality, and durability in microwave absorption. In this study, a sandwich-like graphene-based composite is successfully fabricated by an interfacial engineering of amorphous carbon microspheres (ACMs) and reduced graphene oxide (rGO), with a structure of rGO/ACMs/rGO. The as-prepared rGO/ACMs/rGO composite presents comparable/superior refl ection loss characteristics in the frequency range of 2.0-18.0 GHz to previous composites of graphene and high-density magnetic particles. Electromagnetic parameters and simulation resu...