Fabrication of binary MOF-derived hybrid nanoflowers via selective assembly and their microwave absorbing properties

In recent years, carbon materials derived from metal-organic frameworks (MOFs) have attracted much attention in the field of microwave absorption. It is challenging to prepare composite absorbers with a controllable binary MOF-on-MOF heterostructure. Here, we construct two binary hybrid MOF heterostructures through selective assembly strategies, and realizes their conversion to magnetic porous carbon materials through a simple carbonization process. The special hybrid structure of hexagonal pyramid column and octahedron depends on the selective growth of the guest MOF on the specific crystal facet of the host MOF. The microwave absorbing properties of carbonized UIO-66@Co-doped MIL-88B (UM) and DUT-52@Co-doped MIL-88B (DM) are systematically studied. The selectively combined heterogeneous components endow the absorber with hierarchical pore structures, optimal impedance matching and excellent electromagnetic attenuation capabilities. The products carbonized at 700 °C (UM-700 and DM-700) exhibit superior microwave absorbing properties. It is worth noting that only with a matching thickness of 2 mm, the minimum reflection loss (RLmin) of DM-700 exceeds −65.2 dB, and the effective absorption bandwidth (EAB, RL < −10 dB) covers 4.8 GHz. This work might provide a new strategy for rational design of absorbers with exquisite MOF-on-MOF heterostructures.