Waste Polyethylene-Derived Carbon Dots: Administration of Metal-Free Oxidizing Agents for Tunable Properties and Photocatalytic Hyperactivity
Bramhaiah Kommula, Sagnik Chakraborty, Maqsuma Banoo, Raj Sekhar Roy, Supriya Sil, Abhishek Swarnkar, Bhawna Rawat, Kamalakannan Kailasam, Ujjal K. Gautam
Abstract
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.