Overlooked\nGeneration\nof Reactive Oxidative Species\nfrom Water and Dioxygen by Far UV Light

Far\nUV light at 222 nm (UV<sub>222</sub>) is gaining\nmuch attention\nfor efficient water purification in UV<sub>222</sub> irradiation and\nUV<sub>222</sub>-based advanced oxidation processes (AOPs). The direct\nphotolysis of pollutants is regraded to be their major removal mechanism\nby a sole UV<sub>222</sub> treatment. However, this paper reports\nthe important roles of reactive oxidative species (ROS) generated\nfrom dioxygen and water under only UV<sub>222</sub> radiation. Multiple\nROSs are identified, including hydroxyl radical (HO<sup>·</sup>), singlet oxygen (<sup>1</sup>O<sub>2</sub>), superoxide radical\nanion (<sup>·</sup>O<sub>2</sub><sup>–</sup>), and ozone\n(O<sub>3</sub>). HO<sup><sup>·</sup></sup> is the major ROS for\nthe degradation of 18 organic micropollutants under UV<sub>222</sub> radiation, with an observed quantum yield of 0.447 and the concentration\nof 10<sup>–13</sup> M at pH 7. Dioxygen is the initial source\nof ROS, while water mainly serves as a medium to react with the photolytic\nintermediate of O<sub>3</sub> (i.e., O(<sup>1</sup>D)) to form HO<sup>·</sup>. Water matrix components of HCO<sub>3</sub><sup>–</sup> and natural organic matter can inhibit the HO<sup>·</sup> concentration,\nwhereas NO<sub>3</sub><sup>–</sup> significantly enhances it.\nIn drinking water, UV<sub>222</sub> alone removes 18 micropollutants\nmore efficiently than the typical UV<sub>254</sub>/H<sub>2</sub>O<sub>2</sub> AOP (150 μM), with reduced energy consumption. This\nstudy discloses a novel mechanism of ROS generation in UV<sub>222</sub> irradiation and underscores UV<sub>222</sub> as an emerging chemical-free\nAOP for water purification.