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[Display omitted] • Carbonization and crystallization of feedstock can be achieved by one step in Sc-CO 2. • Iron salt enhanced depolymerization of plastics significantly via catalytic effect. • Sc-CO 2 favored formation of oxygen-rich functional groups on magnetic hybrid surface. • Magnetic Fe 3 O 4 was in-situ anchored in formed carbonaceous pore of bulk char. • Halogen-free magnetic hybrid exhibited excellent capacity for Cr(VI) immobilization. A huge amount of waste halogenated plastics is a considerable resource pool but how to transform these wastes into functional products is always a great technical challenge due to potential release of halogenated dioxin during process. In this study, one type of benign reaction medium-sub/supercritical carbon dioxide (Sc-CO 2) was used for converting halogenated plastics into magnetic carbon-based hybrid along with simultaneous dehalogenation. It was found that Sc-CO 2 treatment coupled with subsistent iron salt adjuvant advantageously inhibited the generation of benzene derivatives with high molecular weight and facilitated growth of pore structure of carbon skeleton with limited production of coke tars. Meanwhile, magnetic Fe 3 O 4 particles were gradually crystallized and eventually encapsulated in ordered mesoporous carbonaceous product to enhance the further carbonization of plastics without any halide residues. Cr(Ⅵ) immobilization tests indicated that as-obtained magnetic hybrid exhibited great adsorption capacity above 157 mg g−1 and the immobilization process was well fit for Langmuir model and pseudo-second-order kinetic model. This study provides a new insight into a cost-effective process for fabrication of magnetic functional hybrid using waste halogenated plastics without release of second pollutants and its versatile application as adsorbents or catalysts. [ABSTRACT FROM AUTHOR]