Divergent Upcycling of Polystyrene into Phenol and Hydroquinone Derivatives by Photocatalysis and Electrocatalysis

The selective upcycling of polystyrene (PS) waste into value-added aromatics has emerged as a compelling strategy toward sustainable plastic valorization, drawing significant scientific and industrial interest. While most existing methods involved oxidative C─C bond cleavage predominantly yield benzoic acid, the direct conversion of waste PS into phenolic compounds remains largely unexplored. Herein, we report the first example of photocatalytic upcycling of PS into phenol derivatives with high chemoselectivity. This economical method proceeds under ambient conditions (1 atm air and room temperature) using an inexpensive organic photocatalyst via photooxidation-induced Hock rearrangement in a single step. The use of strong acid effectively suppresses the formation of benzoic acid, playing a critical role in high selectivity. Experimental and density functional theory (DFT) calculations revealed that the cis configuration of neighboring phenyl rings in PS raises the barrier for hydrogen atom transfer (HAT) from the benzylic C─H bond, thereby contributing to the low polymer conversion. Furthermore, the novel divergent upcycling of PS to hydroquinone derivatives was achieved by a photo-electro tandem strategy. The practicality of this strategy is demonstrated by depolymerization of real-life PS using a sunlight-driven photocatalytic and electrocatalytic degradation platform, underscoring its promising potential for sustainable and scalable upcycling of PS waste.