Surface structure of ferrihydrite: Insights from modeling surface charge
Surface structure of ferrihydrite: Insights from modeling surface charge
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水铁矿的表面结构：表面电荷建模的见解
DOI：
10.1016/j.chemgeo.2016.12.018
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发表时间：
2017
期刊：
影响因子：
3.9
通讯作者：
M. Machesky
中科院分区：
文献类型：
--
作者：
N. Bompoti;M. Chrysochoou;M. Machesky
铁水石膏（FH）由于其大的比表面积和高的反应活性，在控制自然界中许多化合物的命运和运输方面起着重要的作用。这项研究是首次尝试使用最近提出的包含四面体配位Fe原子的表面结构构建表面络合模型（Hiemstra，2013）。测试了该模型描述不同制备方法和不同净质子电荷零点（PZNPC）的FH表面电荷曲线的能力。通常，已经经受老化的FH颗粒较大，并且具有较低的比表面积（SSA）和较高的PZNPC。该结构模型包括仅存在于（1-11）和（1-10）面上的2种单配位（SC）氧和也存在于基面（00 - 1）和（00-1）上的5种三配位（TC）氧，总共11个位点。11位点模型能够模拟PZNPC低于8.5的新鲜FH数据集，但当酸性基底面的贡献最小化时，只能模拟更高的PZNPC。可用的显微镜观察结果不支持该条件，这表明基面上的TC组可能具有高于宏观PZNPC的log K值。我们试图通过三个版本的简化3部位模型来检验这一假设，在（1-10）和（1-11）上使用SC和一个TC，log K 8.0（等于新鲜FH PZNPC），在基底平面上使用一个TC组，log K 9.5。这使得能够通过调整面部贡献来拟合老化FH数据集的PZNPC。一个尚未解决的问题是，该模型是否准确地描述了SC和TC网站的相对贡献的整体电荷，这对准确描述特定的离子吸附的影响。
Ferrihydrite (FH) plays an important role in controlling the fate and transport of many compounds in nature due to its large surface area and high reactivity. This study is the first attempt to build a surface complexation model using the recently proposed surface structure that incorporates tetrahedrally coordinated Fe atoms (Hiemstra, 2013). The ability of the model to describe the surface charge curves of FH with different preparation methods and Points of Zero Net Proton Charge (PZNPC) is tested. In general, FH particles that have been subject to aging are larger and have lower specific surface area (SSA) and higher PZNPCs. The structural model includes 2 types of singly coordinated (SC) oxygens that are present only on the (1-11) and (1-10) faces and 5 types of triply coordinated (TC) oxygens that are also present on the basal planes (001) and (00-1), for a total of 11 sites. The 11 - site model was able to simulate fresh FH datasets with PZNPC lower than 8.5, but could only simulate higher PZNPCs when the contribution of the more acidic basal planes was minimized. The available microscopic observations do not support this condition, which suggests TC groups on the basal planes likely have log K values higher than the macroscopic PZNPC. We attempted to test this hypothesis through three versions of simplified 3-site models, using SC and one TC on (1-10) and (1-11), with log K 8.0 (equal to fresh FH PZNPC) and one TC group on the basal planes with log K 9.5. This enables fitting of the PZNPC of aged FH datasets by adjusting the face contributions. An unresolved issue is whether this model accurately describes the relative contribution of SC and TC sites to the overall charge, which has implications for accurate description of specific ion adsorption.