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

Abstract

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−WOv). 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−WOv 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−WOv 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.