Pyrite-promoted hydrothermal upcycling of polyvinyl chloride waste: Deep dechlorination, enhanced graphitization, and heterogeneous Fenton catalysis.

Green dechlorination and high-value conversion of polyvinyl chloride (PVC) waste are critical challenges in plastic pollution control and resource recycling. This work presents a pyrite (Py)-enhanced one-step hydrothermal strategy that utilizes the reducing ability and Lewis acidity of Py to synergistically promote deep dechlorination and catalytic carbonization of PVC, thereby preparing an efficient heterogeneous Fenton catalyst. The Py-PVC system achieved a dechlorination efficiency of 99.90% at 240°C for 6 h, 15.72% higher than that of the control system without Py. Fe2+ donated electrons to facilitate C-Cl bond cleavage, thereby forming the C=C bond; while lattice sulfur contributed to Fe2+ regeneration. Subsequently, driven by Fe2+/3+ catalysis, the dechlorinated polyene intermediates formed highly graphitized hydrochar. The resulting composite showed excellent heterogeneous Fenton activity, removing 99.2% of bisphenol A within 10 min and facilitating the activation leaching of 84.75% of uranium within 180 min. As an electron shuttle, the graphite-carbon structure not only facilitated the transfer of electrons from Py to recalcitrant organochlorines during the hydrothermal process but also promoted the Fe(III)/Fe(II) cycle during the advanced oxidation process. This work elucidates the synergistic mechanism of Py-assisted PVC hydrothermal dechlorination and catalytic carbonization, offering perspectives on the green upgrading of chlorinated plastics.