Activating Oxygen via the 3-Electron Pathway to Hydroxyl Radical by La-O₄ Single-atom on WO₃ for Water Purification

Shifting photocatalytic oxygen activation towards 3-electron (e^-) pathway to hydroxyl radicals, instead of the normal 1 e^- to superoxide radicals, becomes increasingly important for pollution degradation since hydroxyl radicals possess a high oxidation potential (2.80 V). Here, we demonstrate a selective oxygen activation to hydroxyl radicals via 3 e^- pathway using single atomically dispersed La based on WO₃ fabricated with oxygen vacancies to weaken La-O coordination strength (denoted as LaO₄-WO_v). Unsaturated-state La overcomes the rate-limited step of 2 e^- oxygen reduction reaction towards to hydrogen peroxide via tuning binding free energy of key reaction intermediate *OOH, stepped by easy generation of hydroxyl radicals via 1 e^-. This strategy alters the activation of oxygen process from 1 e^- to 3 e^-. Hydrogen peroxide and hydroxyl radicals over LaO₄-WO_v produces 3.8 and 3.3 mmol L^-1 h^-1, 35 and 8 times that of detected over WO₃, respectively. Rapid and complete removal of tetracycline realizes over LaO₄-WO_v with 0.077 min^-1 of rate constant, 38 times that of WO₃. Degradation efficiencies keep greater than 98 % following five repeats, revealing a practical-utilization-level robust stability. This work builds an unsaturated-state transition metal site for manipulating oxygen activation towards an effective water purification as a representative application.