Polypropylene-Derived Luminescent Carbon Dots

Polypropylene is one of the most challenging plastics to recycle or upcycle due to its excellent chemical and thermal stability. Here, we report an effective two-step synthesis to prepare carbon dots (CDs) from polypropylene (PP). In the first step, bulk PP is converted to PP nanoparticles (PP-NPs) by using a reprecipitation process. In the second step, the PP-NPs are carbonized by a hydrothermal treatment. The size, structure, and photonic properties of the PP-CDs vary significantly with hydrothermal treatment temperature. At higher temperature, the PP-CDs product is ∼2.5 nm in diameter with a quantum yield of 10.3% and is free from unconverted PP. At lower temperature (120 °C), the PP-CDs are large in size (∼70 nm) and exhibit low quantum yield (0.2%). This work demonstrates an effective method to fully convert polypropylene to carbon dots and shows a high degree of tunability in the size, structure, and photonic properties of the product.