Low-Temperature and Catalyst-Free Plasma Synthesis of Plastics-Derived Graphene Quantum Dots

Abstract

The advanced industrial, social, and technological developments in modern society have rendered the production of around 300 million tons of plastic annually, yet only 50% or even less are being recycled. Moreover, the current recycling process is limited to the conversion of plastic wastes (PWs) into hydrocarbon fuels, which also requires the use of high temperatures and energies, long reaction time, and high-cost platinum-based catalysts. Therefore, there is an urgent need to develop a more sustainable and environmentally friendly method to recycle these PWs and possibly into functional materials for diverse applications.We introduce non-equilibrium and low-temperature microplasma technologies to convert PWs into graphene quantum dots (GQDs) at ambient conditions without any additional toxic chemicals, expensive catalysts, and sophisticated vacuum technologies. The reactive species generated by the plasma enables not only rapid deconstruction of PWs into small hydrocarbons moieties, but also simultaneous reconstruction of nanographene domain and nucleation into GQDs. GQDs are zero-dimensional carbon nanomaterials with unique quantum confinement and edge effects, which are hybridized by sp2 carbon in a honeycomb network. The quantum confinement and edge effects bestow GQDs with unique, tunable, and stable photoluminescence (PL) properties. Coupled with the biocompatibility, low toxicity, large surface area, and chemical inertness, GQDs can be employed in various applications, including imaging, sensing, optoelectronics, drug delivery, catalysis, and energy related applications. Nevertheless, the current syntheses of GQDs still need the use of high temperatures, strong acids or reducing agents, long reaction time, and tedious synthesis procedures.Here the utilization of microplasma enables the degradation and conversion of various plastics into functional GQDs with well-controlled structures in one-step at ambient conditions and catalyst-free manner, alleviating the current drawbacks in the GQDs synthesis. Among various PWs, polyethylene terephthalate-derived GQDs (PET-GQDs) exhibit enticing and bright white emission under 365 nm UV irradiation with a Commission Internationale de l’Eclairage 1931 of (0.29, 0.35). Moreover, the colloidal PET-GQDs can be exploited for heavy metal ions detection with a low limit of detection of 8.4 nM, while the composite film state is usable as sensitive temperature tag from 10 – 80 °C and LED panel. Our work provides an insight into the novel technologies for PWs recycling into functional nanomaterials in cost-effective, scalable, and environmentally friendly way.