Controlled Pyrolysis of Polystyrene Using Metal-Organic Frameworks

Chemical recycling of polystyrene (PS), one of the most common and abundant plastic materials manufactured around the globe, is vital for reducing plastic waste, mitigating environmental impacts, and providing economically viable solutions that support a sustainable future. The ongoing efforts in PS degradation promise to enhance this process as a key technology in the transition toward a circular society. However, the highly durable nature of PS, which is composed of only hydrocarbon backbones, hampers the implementation of chemical recycling. Multiple radical mechanisms involved in the pyrolysis of PS cause a broad product distribution, which considerably decreases the recovery of the desired monomer. Here, we show a methodology to realize the highly efficient thermal depolymerization of PS mediated by nanoporous metal-organic frameworks (MOFs). Nanoconfinement of PS into a MOF enables a consolidation of complex degradation pathways in the nanochannels, restraining the formation of undesirable heavy oil components made of styrene oligomers and more selectively generating styrene monomers. By leveraging nanoconfinement effects on polymer degradation, this novel protocol demonstrates remarkable depolymerization behaviors with high scalability and practicality, just by treating MOFs and PS together at elevated temperatures, with the potential to become a game-changing technology in the chemical recycling of plastic waste.