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Page 2 of 15 Ding et al. Soft Sci. 2026, 6, 2

This work presents a new strategy for the rational design of high-performance EM absorbers through the synergistic
optimization of structural architecture and compositional modulation.

INTRODUCTION
Driven by advancements in wireless communication - most notably the large-scale deployment of 5G
networks and Internet of Things (IoT) technologies - a growing diversity of smart devices has emerged,
significantly enhancing daily convenience . However, the intrinsic electromagnetic (EM) emissions of these
[1-6]
systems give rise to EM pollution, which can undermine the operational integrity of precision instruments
and impose non-negligible risks to human health. Accordingly, the rational design of EM metasurfaces and
the microscale engineering of the effective attenuation properties of EM-absorbing materials are widely
acknowledged as effective strategies for mitigating such pollution [7-10] . It is worth noting that the fabrication
of metasurfaces typically depends on emerging technologies such as three-dimensional printing and machine
learning, making their areal cost per square foot prohibitive for large-scale implementation. Consequently,
the microscale modulation of the EM dissipation characteristics of composite powders has become the
dominant approach for developing next-generation microwave-absorbing materials [11-14] . Unfortunately, most
existing particulate systems are now approaching the theoretical limit defined by the Rozanov bound, thus
failing to meet the stringent bandwidth requirements of contemporary applications .
[15]

In recent years, metal-organic frameworks (MOFs) and their derivatives have been the subject of extensive
investigation as EM wave-absorbing media, courtesy of their precisely tunable chemical compositions,
hierarchically porous architectures, and diverse micro-morphologies [16-19] . Specifically, mixed-metal oxides
derived from polymetallic MOFs allow atom-level engineering of crystal structures through deliberate
selection and stoichiometric adjustment of constituent metal ions, thereby enabling straightforward control
over dielectric parameters. Notably, the ultra-dense atomic packing inherent to the spinel lattice confers a
significantly reduced formation energy during low-temperature oxidative pyrolysis of polymetallic MOFs
under ambient air conditions. This makes the spinel phase a thermodynamically favorable and structurally
robust matrix for EM absorption . However, akin to conventional ferrite-type absorbers, the high mass
[20]
fraction typically required to achieve sufficient attenuation has long posed a barrier to practical
implementation. Furthermore, oxide ceramics typically exhibit moderate dielectric constants and limited
dielectric loss, which constrains their ability to achieve strong and broadband absorption within targeted
spectral windows . To bypass the Snock limit and achieve pronounced EM dissipation in the mid-to-high
[21]
gigahertz range, growing attention has been devoted to the construction of spinel/carbon
heterostructures [22,23] . Within these architectures, the unavoidable cation/anion site disorder intrinsic to the
spinel lattice, together with high-density dislocations, grain boundaries, and sub-grain boundaries generated
during pyrolysis, provides abundant polarization and relaxation centers. These centers can be strategically
leveraged to modulate EM attenuation . Correspondingly, indirectly tuning the dielectric and magnetic
[24]
properties of spinel-based absorbers through low-temperature pyrolysis of MOFs with tailored metal nodes
constitutes an effective approach to reducing the minimum reflection loss (RLmin). Post-synthetic etching
and ion-exchange protocols that induce spinel frameworks incorporating mesoporous and macroporous
hierarchies further serve as powerful tools for impedance engineering [25,26] . While extensive research efforts
have focused on reducing the mass loading of spinel-based absorbers to enhance impedance matching, the
synergistic effect of ionic doping and microstructural design on EM performance remains largely
underexplored.

Herein, a systematic strategy combining architectural engineering with compositional regulation was
developed to synthesize the Zn Co Ni Fe O composite. Hollow rhombic dodecahedral cages (ZnCo-RDC)
y
x
1-x
4
2-y
were fabricated using bimetallic MOF ZnCo-zeolitic imidazolate frameworks (ZIFs) as the sacrificial
template and tannic acid (TA) as the etchant. TA played dual core roles in this process. First, it enabled