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Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB
Chemosphere ( IF 8.8 ) Pub Date : 2020-08-29 , DOI: 10.1016/j.chemosphere.2020.128188
Jagannath Biswakarma 1 , Kyounglim Kang 2 , Walter D C Schenkeveld 3 , Stephan M Kraemer 2 , Janet G Hering 4 , Stephan J Hug 5
Affiliation  

Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.



中文翻译:

光生 Fe(II) 对 EDTA 和 DFOB 配体控制的铁(氢)氧化物溶解的催化作用

由于铁(氢)氧化物的溶解度差,铁的生物利用度低限制了土壤和水环境中微生物和植物的生长。以前的研究描述了铁(氢)氧化物在连续光照下的加速溶解,但没有区分光还原溶解和光生 Fe(II) 催化配体控制溶解的非还原过程。在这里,我们展示了在缺氧条件下随后的黑暗时期,短光照(5-15 分钟)加速了配体对铁(氢)氧化物的溶解。纤铁矿 (Lp) 和针铁矿 (Gt) (1.13 mM) 与 50 μM EDTA 或 DFOB 的悬浮液用强度与太阳光相当的 UV-A 光(pH 7.0,碳酸氢盐-CO 2缓冲溶液)。在光照期间,Gt-EDTA 的 Fe(II) 产生率最高;其次是 Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt。在缺氧条件下,光化学产生的 Fe(II) 在随后的黑暗期间将溶解速率提高了 10-40 倍,溶解的 Fe(III) 在 DFOB 和 EDTA 下达到 50 μM。在有氧条件下,溶解速率仅在光照期间增加 3-5 倍。DFOB 溶解的 Fe(III) 在照射 10 小时后达到 35 μM,而 EDTA 在 15 μM 达到峰值,然后降至 2 μM 以下。基于动力学模型解释和讨论观察结果。结果表明,在池塘和湖泊的缺氧底水,或藻类大量繁殖的微环境中,短光照可以通过 Fe(II) 催化的配体控制溶解显着提高铁的生物利用度。在有氧环境中,DFOB 等光稳定配体可以在延长光照期间保持溶液中的 Fe(III)。

更新日期:2020-09-16
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