Nano α-Fe@carbonized arundo donax residue: Porosity engineering for microwave absorption and high-temperature exposure stability

The advancement of 5 G communications and aerospace technologies calls for lightweight, sustainable materials that combine microwave absorption with high-temperature exposure stability. Here, giant reed (Arundo donax L.) residue was converted into carbonized porous Arundo donax (CPA) and α-Fe/CPA composites through carbonization and α-Fe incorporation. The loading-dependent pore/channel evolution observed by SEM/EDS is discussed in relation to possible α-Fe-assisted pore remodeling and Fe-C interfacial regulation. The pristine CPA series and Fe-containing Fe@CPA series showed different performance advantages. CPA-15 delivered the strongest minimum reflection loss (RLmin) of −32.3 dB, whereas Fe30@CPA achieved the widest effective absorption bandwidth (EAB) of 7.6 GHz at a thickness of 1.8 mm, although its RLmin was relatively shallow (-12.2 dB). This distinction indicates that strong attenuation and broadband absorption should be evaluated separately rather than assigned to a single universally optimized sample. Fe30@CPA also exhibited the lowest effective thermal conductivity of 0.034 W m⁻¹ K⁻¹ among all tested samples. TGA further showed that Fe30@CPA retained a much higher residual mass than CPA-15 after heating to 600 °C, indicating improved thermal-weight-retention behavior after α-Fe incorporation. During one-sided high-temperature spray-gun exposure, Fe30@CPA maintained its macroscopic structural integrity while the apparent exposed-surface temperature increased to 441.3 °C after 180 s, indicating heat-transfer resistance and short-term high-temperature exposure stability under the present test conditions. These findings provide a sustainable route for converting agricultural residue into porous carbon/Fe composites and highlight the importance of balancing pore architecture, dielectric-magnetic response, impedance matching, and application-relevant high-temperature exposure stability in multifunctional microwave absorber design.