College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua, 321004, China.
Department of Chemical Engineering, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, P7B 5E1, Canada.
Chemosphere. 2020 Mar;242:125232. doi: 10.1016/j.chemosphere.2019.125232. Epub 2019 Oct 26.
Molecular mechanisms responsible for the filtration behaviors of sodium alginate (SA) in presence of different iron(III) ion concentration were explored in this study. It was found that specific filtration resistance (SFR) of alginate mixtures (1.0 gSA/L) firstly increased and then decreased to a trough with iron(III) concentration increase from 0 to 2.5 mM. Alginate mixture interacting with 0.1 mM iron(III) possessed an SFR as high as 1.65 × 10 m kg, which could be explained by Flory-Huggins lattice theory related with gel filtration. Optical observation showed significant morphology transition (from gel to granular solids) of foulant layers with iron(III) concentration increase. A series of characterizations indicated the change of microstructure, pH and surface charge of alginate mixture with iron(III) concentration. Density functional theory (DFT) simulation suggested that iron(III) ion preferentially forms coordination bonds with three terminal carboxyl groups of alginate chains, facilitating elongation and cross-linking of alginate chains. Such a coordination mode induces formation of a slime and homogeneous gel, corresponding to high SFR. Continuous increase in iron(III) concentration leads to non-terminal coordination, which makes alginate chains more clustered and coiled. This effect, together with effects of the reduced surface charge and electric double layer compression, significantly decrease SFR of alginate mixtures. This study provided deep molecular insights into effects of iron(III) ions on alginate fouling.
本研究探讨了不同铁(III)离子浓度下海藻酸钠(SA)过滤行为的分子机制。结果发现，当铁(III)浓度从 0 增加到 2.5mM 时，海藻酸钠混合物(1.0 gSA/L)的比过滤阻力(SFR)先增加后降低至一个低谷。与 0.1mM 铁(III)相互作用的海藻酸钠混合物的 SFR 高达 1.65×10 m kg，这可以用与凝胶过滤相关的 Flory-Huggins 晶格理论来解释。光学观察表明，随着铁(III)浓度的增加，污垢层的形态发生了显著的转变(从凝胶到颗粒状固体)。一系列的特性表明，随着铁(III)浓度的增加，海藻酸钠混合物的微观结构、pH 值和表面电荷发生了变化。密度泛函理论(DFT)模拟表明，铁(III)离子优先与海藻酸钠链的三个末端羧基形成配位键，促进了海藻酸钠链的伸长和交联。这种配位模式诱导了粘性物和均质凝胶的形成，对应于高 SFR。铁(III)浓度的持续增加导致非末端配位，使海藻酸钠链更加聚集和卷曲。这种效应，加上表面电荷和双电层压缩减少的影响，显著降低了海藻酸钠混合物的 SFR。本研究为铁(III)离子对海藻酸钠污垢的影响提供了深入的分子见解。
