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Zeolitic imidazolate frameworks (ZIFs), a group of metal-organic frameworks (MOFs), hold promise as building blocks in electromagnetic (EM) wave absorbing/shielding materials and devices. In this contribution, we proposed a facile strategy to synthesize three-dimensional ZIF-67-based hierarchical heterostructures through coordinated reaction of a preceramic component, poly(dimethylsilylene)diacetylene (PDSDA) with ZIF-67, followed by carbonizing the PDSDA-wrapped ZIF at high temperature. The introduction of PDSDA leads to controllable generation of a surface network containing branched carbon nanotubes and regional distributed graphitic carbons, in addition to the nanostructures with a well-defined size and porous surface made by cobalt nanoparticles. The surface structures can be tailored through variations in pyrolysis temperatures, therefore enabling a simple and robust route to facilitate a suitable structural surface. The heterostructure of the ZIF nanocomplex allows the existence of dielectric loss and magnetic loss, therefore yielding a significant improvement on EM wave absorption with a minimum reflection coefficient (RC min ) of -50.9 dB at 17.0 GHz at a thickness of 1.9 mm and an effective absorption bandwidth (EAB) covering the full Ku-band (12.0-18.0 GHz).

An energy saving Leidenfrost levitation method is introduced to transport microdroplets with virtually frictionless contact between the liquid and solid substrate. Through microengineering of the heating units, selective areas of the whole substrate can be electrothermally activated. A droplet can be levitated as a result of the Leidenfrost effect and further transported when the substrate is tilted slightly. Selective electroheating produces a uniform temperature distribution on the heating units within 1 s in response to a triggering voltage. Alongside these experimental observations, finite element simulations were conducted to understand the role of substrate thermal conductivity on the temperature profile of the selectively heated substrate. We also generated phase diagrams to verify the Leidenfrost regime for different substrate materials. Finally, we demonstrated the possibility of controlling low friction high speed droplet transportation (∼65 mm/s) when the substrate is tilted (∼7°) by structurally designing the substrate. This work establishes the basis for an entirely new approach to droplet microfluidics.