Effects of Structural Regulation and Impedance Matching Synergy on the Microwave Absorption of Lightweight Graphitic Carbon Nitride Nanosheet/Polyacrylonitrile Composites

Two-dimensional carbon nitride materials such as g-C3N4 have been extensively investigated for microwave absorption, yet their performance is often limited by insufficient dielectric loss and poor impedance matching. In contrast, g-C3N5, an emerging N-rich carbon nitride with higher defect density and a more tunable electronic structure, holds great promise for electromagnetic wave attenuation but has remained largely unexplored. In this work, we engineer dendritic PANI-coated g-C3N5 architectures through an in situ oxidative polymerization strategy that enables simultaneous regulation of dielectric properties and impedance matching. Unlike conventional single-component modification, this structure-guided design constructs efficient conductive pathways while introducing abundant heterogeneous interfaces, thereby achieving a well-balanced synergy between conduction loss and interfacial or dipolar polarization. Benefiting from this cooperative mechanism, the g-C3N5/PANI composite with a mass ratio of 4:1 delivers a minimum reflection loss of −46.79 dB at 2.1 mm and a wide effective absorption bandwidth of 5.53 GHz at 2.5 mm. This study establishes g-C3N5 as a promising next-generation microwave absorber and proposes a generalizable structural-engineering concept for designing lightweight and high-efficiency conductive-polymer composites.