School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 1DF, UK.
Environ Sci Process Impacts. 2018 Jun 20;20(6):977-987. doi: 10.1039/c7em00608j.
Reactions occurring at ferric oxyhydroxide surfaces play an important role in controlling arsenic bioavailability and mobility in natural aqueous systems. However, the mechanism by which arsenite and arsenate complex with ferrihydrite (Fh) surfaces is not fully understood and although there is clear evidence for inner sphere complexation, the nature of the surface complexes is uncertain. In this work, we have used periodic density functional theory calculations to predict the relative energies, geometries and properties of arsenous acid (H3AsO3) and arsenic acid (H3AsO4), the most prevalent form of As(iii) and As(v), respectively, adsorbed on Fh(110) surface at intermediate and high pH conditions. Bidentate binuclear (BB(Fe-O)) corner-sharing complexes are shown to be energetically favoured over monodentate mononuclear complexes (MM(Fe-O)) for both arsenic species. The inclusion of solvation effects by introducing water molecules explicitly near the adsorbing H3AsO3 and H3AsO4 species was found to increase their stability on the Fh surface. The adsorption process is shown to be characterized by hybridization between the interacting surface Fe-d states and the O and As p-states of the adsorbates. Vibrational frequency assignments of the As-O and O-H stretching modes of the adsorbed arsenic species are also presented.
在铁的氢氧化物表面发生的反应在控制天然水系统中砷的生物利用度和迁移性方面起着重要作用。然而，亚砷酸盐和砷酸盐与水铁矿（Fh）表面形成配合物的机制尚未完全了解，尽管有内球络合的明确证据，但表面配合物的性质仍不确定。在这项工作中，我们使用周期性密度泛函理论计算预测了亚砷酸（H3AsO3）和砷酸（H3AsO4），分别为最常见的 As(iii)和 As(v)形式，在中间和高 pH 条件下在 Fh(110)表面上吸附的相对能量、几何形状和性质。结果表明，对于两种砷物种，双齿双核（BB(Fe-O))角共享配合物比单齿单核配合物（MM(Fe-O))更具能量优势。通过在吸附的 H3AsO3 和 H3AsO4 物种附近显式引入水分子来考虑溶剂化效应，发现它们在 Fh 表面上的稳定性增加。吸附过程的特征是相互作用表面 Fe-d 态与吸附剂的 O 和 As p 态之间的杂化。还给出了吸附砷物种的 As-O 和 O-H 伸缩振动模式的振动频率分配。
