Constructing conductively hierarchical Co3Fe7/NC@MWCNTs composites by binary MOF-on-MOF hybrids: A promising approach for boosting microwave absorption

MOFs-derived magnetic carbon-based composites exhibit great application potentials in electromagnetic absorption field. Nowadays, the MOF-on-MOF hybrid materials, constructed by self-assembly of two or more MOFs, gradually become the prevailing precursors for efficient microwave absorbers due to the flexible structure and component design which are beneficial to improving microwave attenuation and optimizing impedance matching. Herein, the binary MOF-on-MOF hybrid templates   MIL-88A@ZIF-67 has been fabricated based on a surfactant-assisted growth strategy, and subsequently thermally converted into the spindle-like Co 3 Fe 7 @NC/magnetic MWCNTs composites (CFM) through a DCDA-assisted carbothermal reduction method. It has been revealed that the carbothermal temperature could not only regulate the crystallinity of Co 3 Fe 7 alloys and magnetism of CFM composites, but also make significant impact on chemical and mesoscopic structure of conductively hierarchical architecture composed by surficial MWCNTs and pyrolytic carbon derived from various ligands of different MOFs. Among the three proposed absorbers in this work, the CFM-700 sample with densest surficial magnetic MWCNTs achieved a satisfied balance between intrinsic microwave consumption and impedance matching due to the magnetic-dielectric synergistic effect. The reflection loss of CFM-700 could keep staying below −20 dB in an ultra-wide range from 3.6 GHz to 18.0 GHz when the thickness varies from 1.3 mm to 5.45 mm. Moreover, the minimum reflection loss of CFM-700 is −68.75 dB at 1.88 mm and the effective absorbing bandwidth could reach 4.72 GHz at only 1.55 mm. It is believed that this work paves an inspiring way to design conductively hierarchical magnetic carbon-based composites with excellent microwave absorption through construction of MOF-on-MOF hybrid structures.