Construction of MOF-derived plum-like NiCo@C composite with enhanced multi-polarization for high-efficiency microwave absorption.

Nowadays, facing the inevitable electromagnetic (EM) pollution caused by many electronic products, it is urgent to develop high-performance microwave absorbing materials. In particular, the bimetallic carbon-based composites derived from MOFs exhibit excellent microwave absorption potential due to their simple preparation, low cost, adjustable morphology and magnetoelectric synergy mechanism. In this work, we successfully prepared plum-like NiCo@C composite by simple solvothermal method and carbonization treatment, which displays strong absorption (-55.4 dB) and wide effective absorption band (EAB, 7.2 GHz) when the loading is 20 wt%. The plum-like structure greatly enriches the non-uniform interface and the structural anisotropy contributes to the dissipation of electromagnetic waves. At the same time, the band hybridization and magnetic coupling of NiCo@C contribute to the coordination of EM characteristics. Overall, this work proves the feasibility of NiCo@C hierarchical composite in the field of microwave absorbing, and provides insight for the development of high-performance absorbers.

Rational construction of hierarchical Co@C@NPC nanocomposites derived from bimetallic hybrid ZIFs/biomass for boosting the microwave absorption.

Nowadays, electromagnetic (EM) radiation poses severe environmental pollution and harm to civilian and military life. To this end, it is urgent to synthesize high-efficiency microwave absorbers in terms of composition and structural design. Herein, we reported a unique hybrid nanostructure with Co particles embedded in hollow carbon polyhedron by a series of synthetic steps including carbonization and pyrolysis. Further, the nanoporous carbon (NPC) derived from wheat flour is coated onto the surface of Co@C polyhedrons, forming a special hierarchical structure (Co@C@NPC), which demonstrates outstanding microwave absorption properties due to the hierarchical porous structure, enhanced interfacial polarization, conduction loss, multi-reflection and matched impedance. Typically, with a 10 wt% filler content, the maximum RL of Co@C@NPC reaches -57.2 dB at 9.6 GHz and the corresponding effective bandwidth is 5.7 GHz (from 7.5 to 13.2 GHz) with an absorber thickness of 3 mm. Besides, the filler loading of 10 wt% is much lower than other reported bio-derived absorbers. In short, the hybrid zeolitic imidazolate frameworks offer a novel idea for constructing hollow carbon skeletons and introducing biomass carbon as a green, low cost and renewable material that enhances the dielectric loss and the synergistic effect between permittivity and permeability.

Facile synthesis of the three-dimensional flower-like ZnFe2O4@MoS2 composite with heterogeneous interfaces as a high-efficiency absorber.

Lightweight and high-efficiency microwave absorbers are determined by structure and composition of materials. In this research, a novel core-shell ZnFe2O4@MoS2 composite with a flower-like heterostructure was synthesized successfully by a facile hydrothermal process. The unique 3D heterostructure (porous ZnFe2O4 and MoS2 nanosheets as core and outer shells, respectively) endows the synthesized sample with high-efficiency electromagnetic wave absorption performance. The exploration of microwave absorption properties reveals that the maximum reflection loss displayed by the ZnFe2O4@MoS2 composite is up to -61.8 dB at 9.5 GHz with a filler content of 20 wt%, and the corresponding effective bandwidth (RL exceeding -10 dB) achieves 5.8 GHz (from 7.2 to 13 GHz). The enhanced microwave absorption performance is benefitted by the porous core-shell structure, intense interfacial polarization, multiple reflections, matched impedance and favorable synergistic effect between ZnFe2O4 core and MoS2 shell. Consequently, this strategy provides inspiration for the design of novel microwave absorber with high-performance.

Design of MOF-derived hierarchical Co@C@RGO composite with controllable heterogeneous interfaces as a high-efficiency microwave absorbent.

Carbon-based composites have triggered tremendous attention in the development of high-efficiency microwave absorbers, due to their compatibility, light weight, and high microwave absorption. However, fabricating carbon-based absorbers with a strong absorption ability in a broad frequency range is challenging. Hence, a facile strategy was used to produce Co@C derived from a zeolitic imidazolate framework (ZIF)@ graphene. The Co@C@RGO composite was obtained by annealing the ZIF67/GO nanocomposite precursor at 650 °C in a nitrogen atmosphere. Due to the magnetic loss induced by the Co particles, the dielectric loss generated by the carbon skeletons and graphene, and the interfacial polarization between the components, the hierarchical composite exhibits superior electromagnetic (EM) wave absorption properties. The optimal reflection loss (RL) of the Co@C@ RGO composite can be up to -67.5 dB at 2.6 mm, and the effective bandwidth (≥-10 dB) is 5.4 GHz (10-15.4 GHz) with a thickness of 2 mm at 20 wt% loading. The dipolar polarization caused by graphene, as well as enhanced impedance matching, synergistic effect and interfacial effect among the components, increase the microwave absorption performance of the composite. This work may open a new path to use the Co@C@RGO composite with its high-efficiency EM wave properties as an absorber.