Defect-Engineered Microwave-Responsive Ni@C Composites From Waste PET for Catalytic Plastic Upcycling

Direct catalytic upcycling of solid plastic waste is challenging owing to its chemical robustness, and existing conversion routes often require harsh conditions or costly catalysts. Here, we develop a circular plastic-to-catalyst-to-product strategy converting waste poly(ethylene terephthalate) (PET) bottles into a microwave-responsive composite catalyst for microwave-assisted catalytic plastic upcycling. First, microwave-assisted PET depolymerization and Ni-MOF nanorod crystallization generate abundant missing-cluster defects, inherited during pyrolysis as lattice-distorted Ni nano-cores and edge dislocations encapsulated within a defective carbon shell (Ni@C). These strain-rich Ni─C heterointerfaces enhance dielectric loss and interfacial polarization under microwave irradiation, promoting local microwave energy dissipation at catalyst-plastic contacts and accelerating peroxymonosulfate (PMS) activation. Coupled microwave-thermal-chemical PMS activation initiates polymer-chain disordering, hydrogen abstraction, and C─C bond scission in high-density polyethylene (HDPE) particles before oxidative functionalization, making it more efficient than oxidation-dominated hydrothermal heating. Spectroscopic and strain-mapping analyses reveal that dislocation-rich Ni cores and carbon defects govern microwave energy dissipation and thus catalytic oxidation reactivity. The optimized Ni@C catalyst achieves up to 96% degradation of HDPE and converts products into valuable liquid hydrocarbons and oxygenates with limited phytotoxicity. Overall, this work integrates waste-derived catalyst design with microwave-assisted plastic conversion, offering a route toward circular plastic upcycling and carbon recovery.