Synergy of Local and Remote Electron Transfer Maintains the Electron Deficiency of Active Sites for Enhanced Photocatalytic Upcycling of Plastic Waste

The photo-oxidation of ethylene glycol (EG) into high-value-added glycolic acid (GA) is of practical significance for poly(ethylene terephthalate) (PET) upcycling. As the key active species, the enrichment of hydroxyl radicals (•OH) is vital for improving the conversion efficiency of EG to GA, which remains a significant challenge. Herein, we proposed a strategy of constructing an electron-deficient active center by introducing F atoms with high electronegativity, which strengthened the adsorption of hydroxyl ions (OH^-) to achieve the enrichment of •OH. As for the photocatalyst of Pd nanoparticles-loaded F-doped TiO₂ hollow spheres (Pd/F-THS), local F atoms (proximal to Pd) directly reduce the electron density of Pd sites via electron cloud polarization under static conditions. Upon light irradiation, both local and remote F atoms could synergistically promote the migration of holes to Pd sites, thereby stabilizing Pd sites in a more electron-deficient state and promoting the adsorption of OH^- through enhanced electrostatic attraction. Meanwhile, the extracted photogenerated holes reacted with adsorbed OH^-, forming an ^•OH-enriched region at the Pd sites. Owing to the presence of an •OH-rich Pd center, Pd/F-THS exhibited excellent performance for EG photo-oxidation. The yield rate and selectivity of GA achieved were 13.5 mmol g^-1 h^-1 and 78.6%, respectively, representing the best performance reported to date.