Reactive halogen radicals in saline water promote photochemically-assisted formation of manganese oxide nanosheets,Environmental Science: Nano

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Reactive halogen radicals in saline water promote photochemically-assisted formation of manganese oxide nanosheets
Environmental Science: Nano ( IF 5.8 ) Pub Date : 2022-07-30 , DOI: 10.1039/d2en00410k
Zhenwei Gao ₁ , Charlie Skurie ₁ , Young-Shin Jun ₁

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Halide ions are naturally abundant in oceans and estuaries. Large amounts of highly saline efflux are also made and discharged to surface water from desalination processes and from unconventional oil and gas recovery. These highly concentrated halides can generate reactive halogen radicals. However, the redox reactions of halogen radicals with heavy metals or transition metals have received little attention. Here, we report undiscovered fast oxidation of manganese ions (Mn²⁺) by reactive halogen radicals. Hydroxyl radicals (˙OH) are produced by nitrate photolysis. While ˙OH radicals play a limited role in the direct oxidation of Mn²⁺, ˙OH can react with halide ions to generate reactive halogen radicals to oxidize Mn²⁺. In addition, more Mn²⁺ was oxidized by bromide (Br) radicals generated from 1 mM Br⁻ than by chloride (Cl) radicals generated from 500 mM Cl⁻. In the presence of Br radicals, the abiotic oxidation rate of Mn²⁺ to Mn(IV)O₂ nanosheets is greatly promoted, showing a 62% increase in Mn²⁺(aq) oxidation within 6 h of reaction. This study advances our understanding of natural Mn²⁺ oxidation processes and highlights unexpected impacts of reactive halogen radicals on redox activities with heavy metals and corresponding nanoscale solid mineral formation in brine. This work suggests a new, environmentally-friendly, and facile pathway for synthesizing MnO₂ nanosheets.

中文翻译：

盐水中的活性卤素自由基促进光化学辅助形成氧化锰纳米片

卤化物离子在海洋和河口中天然丰富。海水淡化过程和非常规油气采收过程中也会产生大量高盐分流出物并排放到地表水中。这些高浓度卤化物会产生活性卤素自由基。然而，卤素自由基与重金属或过渡金属的氧化还原反应很少受到关注。在这里，我们报告了未被发现的锰离子 (Mn ²⁺ ) 被活性卤素自由基快速氧化。羟基自由基 (˙OH) 由硝酸盐光解产生。^{虽然˙OH自由基在Mn 2+}的直接氧化中作用有限，但˙OH可以与卤离子反应生成活性卤素自由基以氧化Mn ²⁺。此外，更多的 Mn ²⁺1 mM Br ^-产生的溴化物 (Br) 自由基比 500 mM Cl ^-产生的氯化物 (Cl) 自由基氧化。在Br自由基存在下，Mn ²⁺到Mn( IV )O ₂纳米片的非生物氧化速率大大提高，反应6小时内Mn ²⁺ (aq) 氧化增加了62%。这项研究加深了我们对天然 Mn ²⁺氧化过程的理解，并强调了活性卤素自由基对重金属氧化还原活性和盐水中相应纳米级固体矿物形成的意外影响。这项工作为合成 MnO _{2提供了一种新的、环境友好的、简便的途径}纳米片。

更新日期：2022-07-30

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