Waste Polyethylene-Derived Carbon Dots: Administration of Metal-Free Oxidizing Agents for Tunable Properties and Photocatalytic Hyperactivity

The possibility of converting waste plastics into carbon dots (CDs) with 100% efficiencies using KMnO 4 has emerged as a significant discovery in mitigating plastic pollution and upcycling. However, the lack of tunability of their properties, viz. aerial O 2 harvesting, light-induced autophagy, and photoactivity using air as a free oxidant, has remained a bottleneck. Besides, the toxicity of KMnO 4 makes the process less sustainable. Attempting to bridge these gaps, herein, we demonstrate the preparation of CDs using polyethylene with enormous controllability of their properties by utilizing less-toxic and metal-residue-free oxidizers, e.g., H 2 O 2, HNO 3, HClO 4, and NaClO. We obtain structurally diverse CDs with controllable luminescent quantum yields (∼0.5–8%), excitonic lifetimes (1.3–2.3 ns), and binding energies (147–290 meV). These CDs exhibit a hugely extended range of molecular O 2 harvesting (∼405–650 μM) with different amounts of strongly and weakly surface-bound O 2 molecules within an estimated ratio of ∼0.77–2.51. Autophagy varied from 14 days to a nearly “no-autophagy” show. We efficiently utilized their oxygen harvesting and photocatalytic abilities to synthesize imine compounds from the corresponding amines in the open air (rate constant of ∼0.055 min –1 ), surpassing the literature efficiencies achieved using an O 2 flow and noble metals. Notably, due to oxygen harvesting by CDs, no additional rate enhancement was observed after O 2 purging, establishing the role of CDs in making free air an excellent oxidizing agent.