Synergistic defect and interface engineering in Fe3O4/rGO Hybrids: Toward high-efficiency microwave absorbers with thickness-adaptive broadband effectiveness

The growing demand for high-efficiency electromagnetic wave absorption and shielding materials has accelerated research into magnetic-carbon hybrid systems. This work presents a facile, environment-tunable, and cost-effective binary composite of Fe₃O₄/reduced graphene oxide (rGO) (FRG), fabricated through a three-step synthesis protocol that integrates ultrasonic dispersion, solvothermal reaction, and freeze-drying processes. Structural characterization confirms the uniform anchoring of Fe₃O₄ nanoparticles (average diameter: 13.05 nm) on rGO surfaces and their intercalation between rGO layers, with freeze-drying enhancing interfacial bonding and lower density of FRG. Defect analysis reveals that FRG exhibits a reduced defect distance (L_D = 3.65 nm) and higher defect density (n_D = 2.45 × 10¹¹) compared to GO, promoting dipole polarization and defect polarization. The electromagnetic absorption performance demonstrates a critical dependence on GO concentration: increasing GO content initially enhances, but eventually degrades performance due to a conductivity-permittivity imbalance. Optimized FRG with 11.25 wt% GO achieves a minimum reflection loss of −49.47 dB at 8.17 GHz (4.00 mm thickness), while a 2.50 mm thick sample exhibits broadband absorption (RL < −10 dB) over 6.19 GHz (11.81–18.00 GHz). Furthermore, increasing FRG loading extends the RL < −20 dB effective bandwidth. This work establishes a scalable strategy for designing lightweight binary microwave absorbers with coupled dielectric/magnetic loss mechanisms.