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Fan et al. Soft Sci 2024;4:43 https://dx.doi.org/10.20517/ss.2024.63 Page 5 of 10

X-band and Ku-band at very low filling contents [Figure 2S].

Table 1 summarizes and compares the EAB, RL and filling rates of MOF derivatives under different
dimensions and morphologies.

MECHANISMS OF MA
When a microwave meets an absorber's surface, it can be absorbed, reflected, or transmitted
[Figure 3A] [48-50] . Deep penetration into the absorber causes microwaves to have multiple reflections on the
inner surfaces, which helps dissipate microwave energy [Figure 3B] [38,51,52] .

Dielectric and magnetic losses are the main forms of microwave energy dissipation. Dielectric loss includes
conductive loss and polarization relaxation loss [Figure 3C] [40,43,44,53-57] . Conductive loss arises from the
[58]
directional movement of free electrons within the medium under an alternating current electric field . In
MOF-derived MAMs, conductivity is enhanced by a strong conductive network due to the directional
motion of charges, especially in 1D and 2D composites.

Polarization relaxation loss involves dipole and interfacial polarization, occurring during the directional
[59]
rearrangement of electrons or molecules in response to an electric field . High-temperature carbonization
introduces new functional groups and defects in MOFs, disrupting electron equilibrium and creating
dipoles. When the electric field changes or disappears, these dipoles are forced to rotate, leading to energy
[60]
conversion and attenuation . The heterogeneous interfaces between MOFs and other materials also
enhance polarization relaxation losses.

In the 2 to 18 GHz band, magnetic losses include hysteresis loss, natural resonance, exchange resonance,
and eddy current effects [Figure 3D] [35,39,55,57,61-63] . Hysteresis loss arises from domain wall movement during
magnetization, while eddy current loss heats the material and causes energy loss [64-66] . Natural resonances
stem from the material's anisotropic field, and exchange resonance occurs in sub-micron or nano-sized
particles.

There are two methods for adjusting magnetic loss in MOF-derived MAMs: introducing magnetic metals or
transforming metal ions via carbonization. The introduction of magnetic metals can cause magnetic losses.
Optimizing experimental conditions allows metal ions to be transformed into metals or metal oxides,
regulating magnetic response to enhance magnetic loss.

CONCLUSION AND PERSPECTIVES
Researchers have developed various efficient MOF derivatives by carefully designing their morphology and
dimensions. However, some issues still need to be addressed.

MOF synthesis strategy
The hydrothermal method is widely employed for preparing MOF precursors; however, its low yield and
high costs pose a barrier to mass production. Therefore, it is urgent to explore a new, cost-effective
preparation method capable of achieving mass production (e.g., the microwave-assisted method).

Development of conductive MOF
Low-conductivity ZIFs are often used as MOF precursors, requiring high-temperature carbonization to
improve MA performance. However, this can lead to structural collapse, hindering further research.
Therefore, it is essential to develop conductive MOFs that can be used directly for absorption.