Conductive Metal–Organic Frameworks with Tunable Dielectric Properties for Boosting Electromagnetic Wave Absorption

Abstract

Metal–organic frameworks (MOFs) manifest enormous potential in promoting electromagnetic wave (EMW) absorption thanks to the tailored components, topological structure, and high porosity. Herein, rodlike conductive MOFs (cMOFs) composed of adjustable metal ions of Zn, Cu, Co, or Ni and ligands of hexahydroxytriphenylene (HHTP) are prepared to attain tunable dielectric properties for a tailored EMW absorption. Specifically, the influences of the cMOFs’ composition, charge transport characteristic, topological crystalline structure, and anisotropy microstructure on dielectric and EMW absorption performance are ascertained, advancing the understanding of EMW attenuation mechanisms of MOFs. The boosted conductive and polarization losses derived from the conjugation effects and terminal groups, as well as shape anisotropy, lead to a prominent EMW absorption of the cMOFs. The Cu-HHTP confers a minimum reflection loss (RLmin) of −63.55 dB at the thickness of 2.9 mm and a maximum effective absorption bandwidth of 5.2 GHz. Moreover, Zn-HHTP showcases the absorption superiority in the S-band (2–4 GHz) with an RLmin of −62.8 dB at a thickness of 1.9 mm. This work not only hoists the mechanistic understanding of the structure–function relationships for the cMOFs but also offers guidelines for preparing functional MOF materials.

Kinetics-mediated assembly assisted precise synthesis of magnetic ordered mesoporous carbon nanospheres for ultra-efficient electromagnetic wave absorption

“…According to Debye relaxation theory, the ε ′ and ε ′′ of EMWAMs are closely connected with conductive loss, dipole polarization, and interfacial polarization. In other words, the dielectric loss mechanism can be basically clarified based on the relationship between ε ′ and ε ′′, as described in the following eqn (1): 85–88 where ε s and ε ∞ denote the static permittivity and relative dielectric permittivity at the high-frequency limit. Obviously, the plot of ε ′′ versus ε ′ (Cole–Cole plot) should consist of a series of semicircles according to eqn (1), which are named Cole–Cole semicircles.…”

High-Performance Microwave Absorption Materials: Theory, Fabrication, and Functionalization

“…There are several kinds of dielectric loss MAMs, including carbon-based materials (e.g., graphene, carbon nanotubes, carbon fiber), silicon-based ceramics (e.g., SiC, Si 3 N 4 ), transition metal sulfides (MoS 2 , WS 2 ), conductive polymers (polypyrrole, polyaniline), , and MOF-derived nanomaterials, etc . This review mainly discusses two typical dielectric loss materials, i.e., carbon-based MAMs and silicon-based ceramic MAMs.…”

Optimizing dielectric polarization for electromagnetic wave attenuation via an enhanced Maxwell–Wagner–Sillars effect in hollow carbon microspheres

“…Currently, highly efficient EMW absorbers not only need to possess a strong absorption strength and broad frequency response bandwidth, but also require the advantages of lightweight and stability. 4,5 However, conventional ferromagnetic-based absorbers are unable to satisfy the specific applications of miniaturized and integrated electronic devices due to their intrinsic heavy weight, band-limited response, and poor corrosion resistance.…”