Reduced Electron Delocalization via Symmetry Breaking at Single-Atom Cobalt Sites for Efficient Photocatalytic Plastic Upcycling.

Direct photocatalytic upcycling of nonbiodegradable plastics using single‑atom catalysts (SACs) remain limited by the symmetric coordination of isolated metal sites, which constrains intermediate binding and charge transfer. Here, we reconstruct the heptazine units of polymeric carbon nitride (PCN) via a salt-induced strategy, transforming S─CoPCN with a predominantly symmetric Co─N4 coordination environment into A─CoPCN featuring predominantly asymmetric Co─N3 configurations. Under white-light irradiation at room temperature and 1 bar O2, A─CoPCN enables the conversion of polystyrene to benzoic acid with a yield of 39.6% and a carbon recovery of 71.6%. Compared with previously reported systems that often require elevated temperatures, high O2 pressures, or external oxidants, this system operates under markedly milder conditions. The catalyst further demonstrates broad applicability across diverse nonbiodegradable plastics, including polystyrene, polyisobutylene, polylactic acid, polypropylene, polyethylene, and polyvinyl acetate. Mechanistic studies combining advanced spectroscopy and density functional theory calculations reveal that symmetry breaking suppresses electron delocalization, upshifts the Co d-band center, and lowers exciton binding energy, thereby facilitating charge separation and transfer, promoting O2 adsorption and activation to generate reactive •O2 - species for efficient plastic upcycling. This work identifies coordination asymmetry as a key design principle for SACs and provides a general strategy for enhancing photocatalytic plastic upcycling.