Waste-derived magnetodielectric susceptor for rapid microwave treatment of phenanthrene-contaminated soil

Microwave treatment can alleviate mass-transfer limitations in soils containing aged polycyclic aromatic hydrocarbons (PAHs), but its efficiency is often constrained by weak and spatially heterogeneous soil-microwave coupling. Coal gasification fine slag (CGS) was upcycled into FeN-CGS, a porous Fe₃O₄-anchored N-doped carbon magnetodielectric susceptor with multiscale heterointerfaces. Phenanthrene (PHE) was used as a model three-ring PAH. Under closed-loop 2.45 GHz irradiation at a probe-monitored setpoint of 80 °C, 10 g kg^-1 FeN-CGS achieved 85.8 ± 1.7% and 90.9 ± 2.0% apparent depletion of extractable PHE after 5- and 10-min nominal holding periods, respectively, substantially exceeding the microwave-only and FeN-CGS-only controls. The operational apparent rate coefficient was 0.631 min^-1, with a rate-coefficient-based synergy index of 3.71. Density functional theory calculations, electromagnetic measurements, and blank-controlled heating tests supported the proposed coupling between favorable PHE adsorption at the graphene-N/Fe₃O₄ (111) interface (E_ads = -1.13 eV) and microwave dissipation through dielectric and magnetic losses. Non-target gas chromatography-mass spectrometry showed no prominent accumulation of new extractable aromatic products, while integrated off-gas trapping showed that the PHE-related C₁₄H₁₀ marker was not a major component of the recovered semivolatile fraction. FeN-CGS retained its thermal and magnetic response after material-only microwave aging. Comparative water extraction showed analyte-dependent changes, including lower Fe, Cu, and As concentrations in coupled-system extracts than in microwave-only extracts. Overall, this study demonstrates a waste-derived magnetodielectric strategy for rapid microwave treatment of PHE-contaminated soil without added oxidants, integrating treatment performance with interfacial affinity-dissipation analysis and pathway-oriented environmental screening.