Photochemical cycling of iron mediated by dicarboxylates: special effect of malonate.
Photochemical cycling of iron mediated by dicarboxylates: special effect of malonate.
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DOI：
10.1021/es901956x
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发表时间：
2010-06
影响因子：
11.4
通讯作者：
Zhaohui Wang;Xi Chen;Hongwei Ji;Wanhong Ma;Chuncheng Chen;Jincai Zhao
中科院分区：
文献类型：
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作者：
Zhaohui Wang;Xi Chen;Hongwei Ji;Wanhong Ma;Chuncheng Chen;Jincai Zhao
在大气沃茨的典型条件下，研究了铁与丙二酸（Mal）配体氧化的光化学氧化还原循环。丙二酸盐表现出显着不同的特点，从草酸盐和其他二羧酸盐（或单羧酸盐）。Fe（III）-Mal络合物（FMCs）具有很强的螯合能力和摩尔吸光系数，但Fe（II）生成效率很低（Phi（Fe（II））= 0.0022 +/-0.0009，300 - 366 nm）。Fe（III）的形态计算表明，Mal能够通过改变Mal的浓度来调节Fe（III）-OH络合物和FMCs两种光活性物种之间的比例。自旋俘获电子自旋共振（ESR）实验证明了（.）CH（2）COOH和（.）OH自由基在较低的总Mal浓度（[Mal]（T））下，但只有（.）CH（2）COOH在较高浓度的丙二酸，提供了强有力的证据丙二酸和OH（-）之间的竞争和随后的不同的光反应途径。一旦FMCs主导Fe（III）形态，则Fe（II）的光生成和光催化氧化将大大减速。Fe（II）的形成和衰变都存在一个诱导期，直到Fe（III）（OH）（2+）物种随着Mal配体耗尽而成为FMCs上的主要Fe（III）形式。提出了Fe（II）光生过程中Mal的猝灭机理。本研究对于加深我们对酸化富碳大气沃茨中铁循环的认识具有重要意义。
Photochemical redox cycling of iron coupled with oxidation of malonate (Mal) ligand has been investigated under conditions that are representative of atmospheric waters. Malonate exhibited significantly different characteristics from oxalate and other dicarboxylates (or monocarboxylates). Both strong chelating ability with Fe(III) and strong molar absorptivities, but much low efficiency of Fe(II) formation (Phi(Fe(II)) = 0.0022 +/- 0.0009, 300-366 nm) were observed for Fe(III)-Mal complexes (FMCs). Fe(III) speciation calculation indicated that Mal is capable of mediating the proportion between two photoactive species of Fe(III)-OH complexes and FMCs by changing the Mal concentration. Spin-trapping electron spin resonance (ESR) experiments proved the formation of both the (.)CH(2)COOH and (.)OH radicals at lower total Mal concentration ([Mal](T)), but only (.)CH(2)COOH at higher concentrations of malonate, providing strong evidence for competition between malonate and OH(-) and subsequent different photoreaction pathways. Once FMCs dominate the Fe(III) speciation, both photoproduction and photocatalyzed oxidation of Fe(II) will be greatly decelerated. There exists an induction period for both formation and decay of Fe(II) until Fe(III)(OH)(2+) species become the prevailing Fe(III) forms over FMCs as Mal ligand is depleted. A quenching mechanism of Mal in the Fe(II) photoproduction is proposed. The present study is meaningful to advance our understanding of iron cycling in acidified carbon-rich atmospheric waters.