Generation of singlet oxygen by 2D Fe3O4-decorated black phosphorus nanosheets to boost photothermal catalytic upcycling of PET wastes

Global plastic production, particularly polyethylene terephthalate (PET), has surged in modern society, yet conventional disposal methods like incineration and landfills pose severe environmental risks. Photothermal catalysis emerges as a sustainable solution, combining photo with thermal catalysis processes to reduce energy consumption while enhancing catalytic efficiency. Herein, we demonstrate a promising approach employing black phosphorus nanosheets (BPNSs) featuring exceptional photothermal conversion and singlet oxygen ( 1 O 2 ) generation to photothermally accelerate PET depolymerization. Integrating with Fe 3 O 4 nanoparticles, the formed covalent P-O bonds shield reactive phosphorus atoms in BPNSs from oxidation to improve their stability, and Fe 3 O 4 enables magnetic recovery and synergy with PET's carbonyl groups. Under solar irradiation, the BPNSs-Fe 3 O 4 composite achieves 98.3 % PET conversion and 95.2 % bis(2-hydroxyethyl) terephthalate (BHET) yield at 185 °C in ethylene glycol, 2.8-fold and 6.5-fold higher than traditional thermal catalysis, respectively. Mechanistic studies reveal that localized photothermal heating and 1 O 2 -driven nucleophilic elimination of ester groups collaboratively enhance the reaction kinetics, reducing the activation energy by 53.7 %. Successful outdoor validation and BHET repolymerization confirm the practicability. This closed-loop photothermal strategy demonstrates excellent efficiency and product quality, offering a viable pathway toward sustainable plastic upcycling with dual environmental and economic potentials.