Arsenite Oxidation Initiated by the UV Photolysis of Nitrite and Nitrate

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• 作者：Dong-hyo Kim ; Jaesang Lee ; Jungho Ryu ; Kitae Kim ; Wonyong Choi
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：April 1, 2014
• 年：2014
• 卷：48
• 期：7
• 页码：4030-4037
• 全文大小：519K
• 年卷期：v.48,no.7(April 1, 2014)
• ISSN：1520-5851

文摘

This study demonstrates that the production of reactive oxidizing species (e.g., hydroxyl radical (鈥H)) during the photolysis of nitrite (NO₂^{鈥?/sup>) or nitrate (NO₃鈥?/sup>) leads to the oxidative conversion of arsenite (As(III)) to arsenate (As(V)). While the direct UV photolytic oxidation of As(III) was absent, nitrite (20 or 200 渭M) addition markedly accelerated the oxidation of As(III) under UV irradiation (位 > 295 nm), which implies a role of NO₂鈥?/sup> as a photosensitizer for As(III) oxidation. Nitrate-mediated photooxidation of As(III) revealed an initial lag phase during which NO₃鈥?/sup> is converted into NO₂鈥?/sup>. UV-Photosensitized oxidation of As(III) was kinetically enhanced under acidic pH condition where nitrous acid (HNO₂) with a high quantum yield for 鈥H production is a predominant form of nitrite. On the other hand, alkaline pH that favors the photoinduced transformation of NO₃鈥?/sup> to NO₂鈥?/sup> significantly facilitated the catalytic reduction/oxidation cycling, which enabled the complete oxidation of As(III) at the condition of [As(III)]/[NO₂鈥?/sup>] 1 and markedly accelerated NO₃鈥?/sup>-sensitized oxidation of As(III). The presence of O₂ and N₂O as electron scavengers enhanced the photochemical dissociation of NO₂鈥?/sup> via intermolecular electron transfer, initiating the oxidative As(III) conversion route probably involving NO₂鈥?and superoxide radical anion (O₂鈥?sup>鈥?/sup>) as alternative oxidants. The outdoor experiment demonstrated the capability of NO₂鈥?/sup> for the photosensitized production of oxidizing species and the subsequent oxidation of As(III) into As(V) under solar irradiation.}