Nanocatalyzed upcycling of the plastic wastes for a circular economy

Plastics are now essential components in our daily life, but they have also raised a waste crisis and environmental pollution issues. The traditional plastic waste treatments rely on high-energy input and are environmentally unfriendly. The emergence of nanocatalyzed chemical upcycling of plastic waste approaches, aiming to convert wastes to value-added chemicals, is encouraging and may enable a circular-plastics economy. Thus, in this Review, we first briefly summarize the background of the plastic waste treatments by introducing the most common plastic types and the traditional treatment methods. We then review the chemical upcycling of plastics in terms of nanocatalyzed pyrolysis, pyrolysis-gasification, solvolysis, hydrocracking and the light/electrochemical-induced processes from a historical account to recent achievements. Coordination chemistry aspects are emphasized in these processes, particularly in the plastics depolymerization mechanism. Emphasis is placed on highlighting the encouraging results recently obtained, especially on the rational design of nanocatalysts with tunable active metals, size, support, and coordination environments for improved catalytic performances. Indications towards further research and applications for value-added products synthesis are also proposed. In addition, some other emerging technologies for waste plastic treatments are introduced. Finally, perspectives for further developments towards a circular-plastic economy are highlighted.