Dzade Nelson Y, Roldan Alberto, de Leeuw Nora H
Department of Earth Sciences, Utrecht University , Princetonplein 9, 3584 CC, Utrecht, The Netherlands.
School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 1DF, United Kingdom.
Environ Sci Technol. 2017 Mar 21;51(6):3461-3470. doi: 10.1021/acs.est.7b00107. Epub 2017 Mar 10.
Reactive mineral-water interfaces exert control on the bioavailability of contaminant arsenic species in natural aqueous systems. However, the ability to accurately predict As surface complexation is limited by the lack of molecular-level understanding of As-water-mineral interactions. In the present study, we report the structures and properties of the adsorption complexes of arsenous acid (As(OH)) on hydrated mackinawite (FeS) surfaces, obtained from density functional theory (DFT) calculations. The fundamental aspects of the adsorption, including the registries of the adsorption complexes, adsorption energies, and structural parameters are presented. The FeS surfaces are shown to be stabilized by hydration, as is perhaps to be expected because the adsorbed water molecules stabilize the low-coordinated surface atoms. As(OH) adsorbs weakly at the water-FeS(001) interface through a network of hydrogen-bonded interactions with water molecules on the surface, with the lowest-energy structure calculated to be an As-up outer-sphere complex. Compared to the water-FeS(001) interface, stronger adsorption was calculated for As(OH) on the water-FeS(011) and water-FeS(111) interfaces, characterized by strong hybridization between the S-p and O-p states of As(OH) and the surface Fe-d states. The As(OH) molecule displayed a variety of chemisorption geometries on the water-FeS(011) and water-FeS(111) interfaces, where the most stable configuration at the water-FeS(011) interface is a bidentate Fe-AsO-Fe complex, but on the water-FeS(111) interface, a monodentate Fe-O-Fe complex was found. Detailed information regarding the adsorption mechanisms has been obtained via projected density of states (PDOS) and electron density difference iso-surface analyses and vibrational frequency assignments of the adsorbed As(OH) molecule.
活性矿泉水界面控制着天然水系统中污染物砷物种的生物有效性。然而，由于缺乏对砷-水-矿物相互作用的分子水平理解，准确预测砷表面络合的能力受到限制。在本研究中，我们报告了通过密度泛函理论（DFT）计算得到的亚砷酸（As(OH)₃）在水合硫铁矿（FeS）表面吸附络合物的结构和性质。给出了吸附的基本方面，包括吸附络合物的配准、吸附能和结构参数。正如预期的那样，FeS表面通过水合作用得以稳定，因为吸附的水分子稳定了低配位的表面原子。As(OH)₃通过与表面水分子形成氢键网络，在水-FeS(001)界面上弱吸附，计算得出的最低能量结构为As朝上的外层络合物。与水-FeS(001)界面相比，计算得出As(OH)₃在水-FeS(011)和水-FeS(111)界面上的吸附更强，其特征是As(OH)₃的S-p和O-p态与表面Fe-d态之间有强烈的杂化。As(OH)₃分子在水-FeS(011)和水-FeS(111)界面上呈现出多种化学吸附几何构型，在水-FeS(011)界面上最稳定的构型是双齿Fe-AsO-Fe络合物，但在水-FeS(111)界面上，发现的是单齿Fe-O-Fe络合物。通过态密度投影（PDOS）、电子密度差等值面分析以及吸附的As(OH)₃分子的振动频率归属，获得了有关吸附机制的详细信息。
