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Hydrothermal Fenton-like process for dehydrochlorination and recovering of PVC pipe microplastics in aquatic systems
Summary
Researchers developed a hydrothermal Fenton-like process that achieved over 99% dechlorination of PVC microplastics under subcritical water conditions. The process converted the plastic into solid carbon products that retained most of the original carbon content and showed potential for conversion into graphene. The study provides a promising approach for both neutralizing the environmental hazards of PVC microplastics and recovering valuable carbon materials.
The widespread use of polyvinyl chloride (PVC) pipes in plumbing and drainage systems constitutes a major source of microplastic (MPs) pollution in aquatic environments. Both discarded pipes and the derived PVC_MPs present serious environmental and health risks. To be addressed, this study presents a Fenton-like strategy using 1.0wt%HO with Fe(OH) under subcritical water (250°C, ∼3.0MPa), achieving near-complete dehydrochlorination (>99.0% efficiency) of PVC_MPs. The generated solid carbonaceous products retained most of carbon from PVC_MPs (89.27± 0.26 %), demonstrating their great potential for valuable conversion into graphene. Liquid phase product was primarily consisted of Fe/Fe and monocyclic aromatics (e.g.benzaldehyde and acetophenone). Mechanistic investigations revealed that Fe(OH) initially served as an interfacial catalyst and adsorbent, facilitating critical bonds cleavage. Subsequent release of HCl promotes the dissolution of Fe ions, activating Fenton-like reactions to generate abundant reactive oxygen species (ROS), primarily HO·, HO· and O. These ROS radicals drive dehydrochlorination via β-scission, where the attack on C-H bonds generates alkyl radicals (R·) as key intermediates to proceed subsequent dehydrochlorination, oxygenation, and dehydrogenative aromatization. The resulting C=C bonds by dehydrochlorination enabled further cyclization and dehydroaromatization. This proposed mechanism is strongly supported by molecular dynamics simulations and density functional theory calculations. Techno-economic analysis demonstrated a remarkable net revenues of 4331.86 USD per ton of PVC pipes through the graphene recovering pathway. Therefore, this Fenton-like strategy not only help mitigate PVC (micro)plastic pollution in aquatic systems but also offers an economically attractive pathway for (micro)plastic wastes managements in future.