Synergistic Photogeneration of Reactive Oxygen Species by Dissolved Organic Matter and C_(60) in Aqueous Phase

摘要

We investigated the photogeneration of reactive oxygen species (ROS) by C_(60) under UV irradiation, when humic acid (HA) or fulvic acid (FA) is present. When C_(60) and dissolved organic matter (DOM) were present as a mixture, singlet oxygen (~1O_2) generation concentrations were 1.2-1.5 times higher than the sum of ~1O_2 concentrations that were produced when C_(60) and DOM were present in water by themselves. When C_(60) and HA were present as a mixture, superoxide radicals (O_2~(•-)) were 2.2-2.6 times more than when C_(60)and HA were present in water by themselves. A synergistic ROS photogeneration mechanism involved in energy and electron transfer between DOM and C_(60) was proposed. Enhanced ~1O_2 generation in the mixtures was partly due to ~3DOM~* energy transfer to O_2. However, it was mostly due to ~3DOM~* energy transfer to C_(60) producing ~3C_(60)~*. ~3C_(60)~* has a prolonged lifetime (＞4 μs) in the mixture and provides sufficient time for energy transfer to O_2, which produces ~1O_2. The enhanced O_2~(•-) generation for HA/C_(60) mixture was because ~3C_(60)~* mediated electron transfer from photoionized HA to O_2. This study demonstrates the importance of considering DOM when investigating ROS production by C_(60).