Preparation of laminated CuSe/Cu-MOF gradient hybrids with a conductive-Island/insulative-sea structure for broadband microwave absorption

Materials must achieve an ideal balance between low surface reflection and high internal dissipation in electromagnetic wave (EMW) absorption. CuSe shows great potential in EMW absorption due to its excellent electrical conductivity and optical absorption properties, but it suffers from impedance mismatch caused by an excessively high real part of dielectric constant (ε′), leading to strong surface reflection and limiting both the effective absorption bandwidth and matching thickness. Cu-MOF with a low ε′ (~ 4.4) and porous structure was introduced as a “dielectric buffer layer”. The EMW performance of the CuSe/Cu-MOF laminate, combining the high-loss characteristics of CuSe with the buffering effect of Cu-MOF, can be significantly improved. Therefore, gradient heterostructures of CuSe/Cu-MOF laminates are fabricated in situ via a two-step hydrothermal route, and 500 nm hexagonal CuSe nanosheets (conductive islands) are dispersed within a 3D porous matrix of 20 µm octahedral Cu-MOF (insulating seas). A minimum reflection loss of –41 dB was recorded at 10.4 GHz with 3.5 mm thickness and a CuSe content of 25 wt% (75 wt% Cu-MOF), and an effective absorption bandwidth (RL ≤ –10 dB) extended from 8.2 to 11.2 GHz, which exhibits a reduced ε′ of 9 and a corresponding increase in normalized input impedance (|Zin/Z₀|) to approximately 0.9, indicating significantly improved impedance matching. Meanwhile, interfacial polarization and multiple-scattering mechanisms are synergistically enhanced, effectively prolonging the EMW attenuation path. This method yields gram-scale batches with < 2 g·cm⁻³ density and broad effective bandwidth at a few-millimetre thickness, offering a potentially scalable route toward lightweight microwave absorbers.