Iodate in calcite and vaterite: Insights from synchrotron X-ray absorption spectroscopy and first-principles calculations
Iodate in calcite and vaterite: Insights from synchrotron X-ray absorption spectroscopy and first-principles calculations
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DOI：
10.1016/j.gca.2016.11.032
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发表时间：
2017-02
影响因子：
5
通讯作者：
Jiban Podder;Jinru Lin;W. Sun;S. Botis;J. Tse;N. Chen;Yongfeng Hu;D. Li;J. Seaman;Yuanming Pan
中科院分区：
文献类型：
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作者：
Jiban Podder;Jinru Lin;W. Sun;S. Botis;J. Tse;N. Chen;Yongfeng Hu;D. Li;J. Seaman;Yuanming Pan
碳酸钙（如方解石）是自然界中无机碘的主要宿主，对污染水中放射性碘同位素（129I和131i）的保留和去除可能很重要。然而，人们对碳酸盐中碘的结构环境知之甚少。本研究在常温常压下，采用凝胶扩散法制备了三种浓度（0.002、0.004、0.008 M）、pH值为9.0的naio3掺杂方解石和水晶石。电感耦合等离子体质谱（ICP-MS）分析表明，碘优先被纳入方解石，而不是水晶石。同步加速器碘k边x射线吸收近边结构（XANES）光谱证实，IO3−是合成方解石和水晶石中的优势碘种。对碘k边扩展x射线吸收精细结构（EXAFS）数据的分析，加上密度功能理论（DFT）水平上的周期性第一性原理计算，表明方解石和水晶石中IO3−基团的I5+离子分别由三个和两个额外的O原子（即配位数= 6和5）结合，并通过带电耦合取代I5++ Na+↔C4++ Ca2+结合。在最近的Ca2+位点上的Na+阳离子是能量最有利的构型。
Calcium carbonates such as calcite are the dominant hosts of inorganic iodine in nature and are potentially important for the retention and removal of radioactive iodine isotopes (129I and131I) in contaminated water. However, little is known about the structural environment of iodine in carbonates. In this study, iodate (IO3−) doped calcite and vaterite have been synthesized using the gel-diffusion method at three NaIO3concentrations (0.002; 0.004; 0.008 M) and a pH value of 9.0, under ambient temperature and pressure. Inductively coupled plasma mass spectrometry (ICP-MS) analyses show that iodine is preferentially incorporated into calcite over vaterite. Synchrotron iodine K-edge X-ray absorption near-edge structure (XANES) spectra confirm that IO3−is the dominant iodine species in synthetic calcite and vaterite. Analyses of iodine K-edge extended X-ray absorption fine structure (EXAFS) data, complemented by periodic first-principles calculations at the density functional theory (DFT) levels, demonstrate that the I5+ion of the IO3−group in calcite and vaterite is bonded by three and two additional O atoms (i.e., coordination numbers = 6 and 5), respectively, and is incorporatedviathe charged coupled substitution I5++ Na+↔ C4++ Ca2+, with the Na+cation at a nearest Ca2+site being the most energetically favorable configuration.