Adsorption of Cu(II) to ferrihydrite and ferrihydrite-bacteria composites: Importance of the carboxyl group for Cu mobility in natural environments
Adsorption of Cu(II) to ferrihydrite and ferrihydrite-bacteria composites: Importance of the carboxyl group for Cu mobility in natural environments
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DOI：
10.1016/j.gca.2012.06.012
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发表时间：
2012-09-01
影响因子：
5
通讯作者：
Peacock, Caroline L.
中科院分区：
文献类型：
--
作者：
Moon, Ellen M.;Peacock, Caroline L.
细菌相关的铁（氢）氧化物复合物广泛存在于自然环境中，并且与孤立的铁（氢）氧化物和细菌类似，是溶解的痕量金属的重要清除剂。我们通过快速Fe（III）水解沉淀水铁矿，在不存在和存在非Fe代谢的革兰氏阳性细菌枯草芽孢杆菌的情况下，枯草芽孢杆菌通常存在于天然沃茨、土壤和沉积物中。结合XRD、SEM、BET和Fe K-edge EXAFS对复合材料的矿物学、形貌和结晶度进行了研究。我们发现，矿物部分的复合材料是不变的原生矿物学，形态和结晶度相比，纯水铁矿。然后，我们测量了Cu对水铁矿和铁铁矿-B的吸附。枯草杆菌复合材料作为pH值和铁铁矿：细菌的复合材料的质量比的函数，并使用EXAFS来确定铜吸附的分子机制。本文首次直接测定了铁铁矿-B对Cu的吸收。枯草杆菌复合物是吸附到水铁矿和B两者的结果。枯草杆菌级分B对Cu的吸附。枯草芽孢杆菌组分导致在低pH范围（pH类似于4，类似于[Cu]（总）的20%）中显著的Cu吸收，并且在中等pH范围中显著增强的Cu吸收。这种复合材料的吸附行为是在鲜明的对比，纯水铁矿，其中铜吸附是可以忽略不计的低pH值。总体而言，复合材料的主要由水铁矿或B。枯草杆菌，细菌馏分是专门负责在低pH值的铜吸附，而水铁矿馏分主要是负责在高pH值的吸附。此外，随着细菌的质量比的增加，铜吸附到细菌馏分的优势持续到中pH值制度，并显着延伸到上pH值区域。因此，总吸附的Cu之间的复合馏分的分布是pH值和的复合物的水铁矿：细菌的质量比的函数。EXAFS结果表明，Cu以（CuO_4 H_n）（n - 6）双齿共边络合物的形式吸附在水铁矿上;以（CuO_（5）H_n）（n - 8）单齿络合物的形式吸附在水铁矿复合物上，细菌组分上的羧基表面官能团与水铁矿组分上的双齿共边络合物结合。我们的新结果结合以前的工作，铜吸附细菌，腐殖物质和铁（氢）氧化物涂腐殖酸，证明了在自然环境中的铜吸附和流动性的羧基部分的普遍重要性。综上所述，这些结果表明，铜的羧基结合是主要的机制，通过它与非生物和生物有机质相互作用，并提供了一个无处不在的控制自然沃茨，土壤和沉积物中的铜的命运和流动性。我们的研究结果表明，在环境中，一个显着的比例铁（氢）氧化物与有机馏分密切混合，我们必须考虑铜封存这些复合材料除了纯矿物相。(C)2012爱思唯尔有限公司保留所有权利。
Bacterially associated iron (hydr)oxide composites are widespread in natural environments, and by analogy with isolated iron (hydr) oxides and bacteria, are important scavengers of dissolved trace-metals. We precipitated ferrihydrite via rapid Fe(III) hydrolysis in the absence and presence of the non-Fe metabolising, Gram-positive bacterium Bacillus subtilis, commonly found in natural waters, soils and sediments. We combined XRD, SEM, BET and Fe K-edge EXAFS to examine the mineralogy, morphology and crystallinity of the ferrihydrite composites. We find that the mineral fraction of the composites is unaltered in primary mineralogy, morphology and crystallinity compared to pure ferrihydrite. We then measured the adsorption of Cu to ferrihydrite and the ferrihydrite-B. subtilis composites as a function of pH and the ferrihydrite: bacteria mass ratio of the composites, and used EXAFS to determine the molecular mechanisms of Cu adsorption. We determine directly for the first time that Cu uptake by ferrihydrite-B. subtilis composites is the result of adsorption to both the ferrihydrite and B. subtilis fractions. Adsorption of Cu by the B. subtilis fraction results in significant Cu uptake in the low pH regime (pH similar to 4, similar to 20% of [Cu](total)) and significantly enhanced Cu uptake in the mid pH regime. This composite sorption behaviour is in stark contrast to pure ferrihydrite, where Cu adsorption is negligible at low pH. Overall, for composites dominated by either ferrihydrite or B. subtilis, the bacterial fraction is exclusively responsible for Cu adsorption at low pH while the ferrihydrite fraction is predominantly responsible for adsorption at high pH. Furthermore, with an increased mass ratio of bacteria, the dominance of Cu adsorption to the bacterial fraction persists into the mid pH regime and extends significantly into the upper pH region. As such, the distribution of the total adsorbed Cu between the composite fractions is a function of both pH and the ferrihydrite: bacteria mass ratio of the composite. EXAFS shows that Cu adsorbs to ferrihydrite as an inner-sphere, (CuO4Hn)(n - 6) bidentate edge-sharing complex; and to ferrihydrite composites as an inner-sphere, (CuO(5)Hn)(n - 8) monodentate complex with carboxyl surface functional groups present on the bacterial fraction plus the bidentate edge-sharing complex on the ferrihydrite fraction. Our new results combined with previous work on Cu sorption to bacteria, humic substances and iron (hydr) oxides coated with humics, demonstrate the universal importance of the carboxyl moiety for Cu sorption and mobility in natural environments. Taken together these results show that Cu-carboxyl binding is the predominant mechanism by which Cu interacts with abiotic and biotic organic matter, and provides a ubiquitous control on Cu fate and mobility in natural waters, soils and sediments. Our results indicate that in environments where a significant proportion of iron (hydr) oxides are intimately intermixed with an organic fraction, we must consider Cu sequestration by these composites in addition to pure mineral phases. (C) 2012 Elsevier Ltd. All rights reserved.