The adsorption and retention of metal ions to nanoscale iron (hydr)oxides in aqueous systems is significantly influenced by prevailing environmental conditions. We examined the influence of sulfate, the second most common anion in seawater that is present in many other natural aquatic systems, on the adsorption and retention of Cu(II) and Zn(II) to synthetic iron oxyhydroxide nanoparticles (NPs) and their aggregates. Batch uptake experiments with monodisperse NPs and NPs aggregated by changes in pH, ionic strength, and temperature were conducted over sulfate concentrations ranging from 0 to 0.30 M. The introduction of 0.03 M sulfate significantly increased the initial adsorption and retention of Zn(II) and Cu(II) compared to sulfate-free conditions; with increasing sulfate >0.03 M, Zn(II) retention continuously increased, while Cu(II) retention was considerably more variable but increased slightly. NP aggregation, when induced by pH and ionic strength, was positively correlated with metal ion retention, while aggregation temperature was negatively correlated with both adsorption and retention. Aqueous geochemical modeling indicated that Zn(II) readily complexes with sulfate to form ZnSO (aq), but that stable aqueous CuSO species are uncommon. EXAFS spectroscopic analysis suggests structural incorporation of Zn(II) and Zn(II)-sulfate ternary surface complexation, while Cu(II) primarily forms inner-sphere bidentate surface complexes. Collectively, the effects of sulfate in both reducing surface charge repulsion, initiating ternary surface complexation, and enabling structural incorporation aid to enhance both metal adsorption and retention to iron oxyhydroxide NPs and their aggregates.

中文翻译：

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硫酸盐增强分散和聚集的羟基氧化铁纳米颗粒对 Cu(II) 和 Zn(II) 的吸附和保留

水性系统中纳米级氧化铁（氢氧化物）对金属离子的吸附和保留受到当前环境条件的显着影响。我们研究了硫酸盐（存在于许多其他天然水生系统中的海水中第二常见的阴离子）对合成羟基氧化铁纳米颗粒 (NP) 及其聚集体吸附和保留 Cu(II) 和 Zn(II) 的影响。在 0 至 0.30 M 硫酸盐浓度范围内，对单分散 NP 和通过改变 pH、离子强度和温度而聚集的 NP 进行了批量吸收实验。0.03 M 硫酸盐的引入显着增加了 Zn(II) 和 Zn(II) 的初始吸附和保留。 Cu(II) 与无硫酸盐条件相比；随着硫酸盐的增加 >0.03 M，Zn(II) 保留量不断增加，而 Cu(II) 保留量的变化明显更大，但略有增加。当 pH 和离子强度诱导时，纳米粒子聚集与金属离子保留呈正相关，而聚集温度与吸附和保留呈负相关。水相地球化学模型表明，Zn(II) 很容易与硫酸盐络合形成 ZnSO (aq)，但稳定的水相 CuSO 物质并不常见。 EXAFS 光谱分析表明，Zn(II) 和 Zn(II)-硫酸盐三元表面络合结构并入，而 Cu(II) 主要形成内球二齿表面络合物。总的来说，硫酸盐在减少表面电荷排斥、引发三元表面络合以及实现结构掺入方面的作用有助于增强金属对羟基氧化铁纳米颗粒及其聚集体的吸附和保留。