Synergistic sulfur regulation and interface engineering in MOF-derived hierarchical hollow NiCo@NCNTs/S for efficient microwave absorption.

Although MOF-derived materials are promising candidates for microwave absorption, precisely regulating their electromagnetic behavior through microstructure engineering remains a considerable challenge. Herein, a synergistic strategy integrating hollow hierarchical architectures with heteroatom doping is implemented to overcome this limitation. Hollow NiCo-BTC microspheres were employed as the precursor and subjected to calcination in the presence of melamine, which induced the in-situ growth of carbon nanotubes on the surface to form hierarchical hollow NiCo@NCNTs architectures. Subsequent sulfur doping via chemical vapor deposition (CVD) yielded NiCo@NCNTs/S composites with tunable sulfur contents. The hollow architecture significantly enhanced impedance matching and facilitated multiple scattering of microwave within the structure. The hierarchical nanostructures constructed abundant heterogeneous interfaces, effectively augmenting interfacial polarization. Crucially, the coexistence of surface sulfoxides, thiophenic sulfur, and structural defects synergistically modulates the electronic structure. This multi-faceted regulation elevates free electron density while introducing additional dipole and defect-induced polarization centers, thereby establishing an optimal equilibrium between conduction loss and polarization loss. Consequently, the optimized NiCo@NCNTs/S-5 composite exhibited exceptional microwave absorption performance, achieving a maximum reflection loss of -39.73 dB and an effective absorption bandwidth of 4.56 GHz with a thin thickness. This work elucidates a rational design paradigm for MOF-derived absorbers through hollow-hierarchical morphology control and heteroatom doping regulation, offering a viable pathway toward high-performance microwave absorption for practical applications.