NC@TiO₂ microwave-absorber microspheres: control of shell thickness and evaluation of electromagnetic performance

The enhancement of microwave-absorbing properties in carbon materials is often constrained by their homogeneous composition and impedance mismatching. This work proposes a strategy to increase the heterogeneous interface and improve the impedance matching by introducing the TiO₂ transition layer on carbon materials. Polyacrylonitrile (PAN) microspheres were synthesized via one-step precipitation polymerization as nitrogen-doped carbon (NC) precursors. Subsequently, core-shell structured TiO₂-coated NC microwave-absorbing agents (NC@TiO₂) were fabricated through a sequential process involving acidification, directed hydrolysis, and carbonization treatments. The study systematically investigated the effects of varying the feeding ratio of PAN to tetrabutyl titanate (TBT) on the morphology, composition, and microwave-absorbing properties of the resulting materials. When the volume-to-mass ratio of TBT to PAN was 0.125:1, the composite exhibited a minimum reflection loss of −63.8 dB and an effective absorption bandwidth (EAB) of 5.7 GHz at a thickness of 2.5 mm. Adjusting the thickness to 1.8 mm extended the EAB to 6.2 GHz. Our study suggests that semiconducting transition layers have an excellent effect on the microwave absorption performance of carbon materials, and the appropriate thickness can significantly improve the loss capability of the material. This work provides a feasible reference for designing other carbon-based microwave-absorbing materials.