Photothermal catalysis: Recycling polymer to monomer with carbon quantum dots

Plastic recycling strategies to combat rapidly increasing waste build-up are of utmost environmental importance. Because of inherent limitations to mechanical recycling, chemical recycling to monomer has emerged as a powerful alternative that enables infinite recyclability through depolymerization. Regeneration of monomer starting materials allows for the reproduction of virgin polymer in a closed-loop fashion. However, methods for chemical recycling to monomer typically rely on bulk heating of polymer, which leads to unselective depolymerization in complex polymer mixtures and the formation of degradation byproducts. Here, we report a selective chemical recycling strategy facilitated by photothermal carbon quantum dots under visible light irradiation. Upon photoexcitation, we found that carbon quantum dots generate thermal gradients that induce bulk depolymerization of various polymer classes, including commercial samples. This method also provides selective depolymerization in mixed polymer waste streams enabled by the spatial control over thermal gradients. Broadly, photothermal catalysis enables thermally mediated bond cleavages, and subsequent depolymerization, with high selectivity, akin to other photocatalytic processes.