Zinc K-edge X-ray absorption near-edge structure (XANES) spectroscopy of Zn adsorbed to silica and Zn-bearing minerals, salts and solutions was conducted to explore how XANES spectra reflect coordination environment and disorder in the surface to which a metal ion is sorbed. Specifically, XANES spectra for five distinct Zn adsorption complexes (Zn_ads) on quartz and amorphous silica [SiO_2(am)] are presented from the Zn–water–silica surface system: outer-sphere octahedral Zn_ads on quartz, inner-sphere octahedral Zn_ads on quartz, inner-sphere tetrahedral Zn_ads on quartz, inner-sphere octahedral Zn_ads on SiO_2(am) and inner-sphere tetrahedral Zn_ads on SiO_2(am). XANES spectral analysis of these complexes on quartz versus SiO_2(am) reveals that normalized peak absorbance and K-edge energy position generally decrease with increasing surface disorder and decreasing Zn–O coordination. On quartz, the absorption-edge energy of Zn_ads ranges from 9663.0 to 9664.1 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On SiO_2(am), the absorption-edge energy of Zn_ads ranges from 9662.3 to 9663.4 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On both silica substrates, octahedral Zn_ads presents a single K-edge peak feature, whereas tetrahedral Zn_ads presents two absorbance features. The energy space between the two absorbance peak features of the XANES K-edge of tetrahedral Zn_ads is 2.4 eV for Zn on quartz and 3.2 eV for Zn on SiO_2(am). Linear combination fitting of samples with a mixture of Zn_ads complex types demonstrates that the XANES spectra of octahedral and tetrahedral Zn_ads on silica are distinct enough for quantitative identification. These results suggest caution when deciphering Zn speciation in natural samples via linear combination approaches using a single Zn_ads standard to represent sorption on a particular mineral surface. Correlation between XANES spectral features and prior extended X-ray absorption fine structure (EXAFS) derived coordination environments for these Zn_ads on silica samples provides insight into Zn speciation in natural systems with XANES compatible Zn concentrations too low for EXAFS analysis.

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XANES 反映了吸附在二氧化硅上的锌的配位变化和潜在的表面无序

对吸附在二氧化硅和含锌矿物、盐和溶液上的锌进行锌K边 X 射线吸收近边结构 (XANES) 光谱研究，以探索 XANES 光谱如何反映金属离子表面的配位环境和无序被吸附。具体来说，石英和无定形二氧化硅 [SiO _2(am) ]上五种不同 Zn 吸附复合物 (Zn _ads ) 的XANES 光谱来自 Zn-水-二氧化硅表面系统：石英上的外球八面体 Zn _ads，内球八面体Zn_吸附在石英上，内球体四面体Zn_吸附在石英上，内球八面体Zn_吸附在SiO _2(am)上和内球四面体 Zn_吸附在 SiO _{2(am) 上}。对石英上的这些配合物与 SiO _{2(am) 的}XANES 光谱分析表明，归一化峰值吸光度和K边缘能量位置通常随着表面无序度的增加和 Zn-O 配位的降低而降低。在石英上，对于以四面体和八面体配位物种为主的样品，Zn _ads的吸收边缘能量范围分别为 9663.0 到 9664.1 eV。在SiO _2（AM） ，锌的吸收边缘能量_的广告范围为9662.3至9663.4电子伏特用于通过四面体对八面体配位物种分别为主，样品。在两种二氧化硅基材上，八面体 Zn_ads呈现单个K边缘峰特征，而四面体 Zn _ads呈现两个吸光度特征。的XANES的两个吸收峰的特征之间的能量空间ķ四面体的Zn _edge时_广告是为2.4eV为锌对石英和为3.2eV为锌在SiO _2（AM） 。样品与 Zn _ads复合类型混合物的线性组合拟合表明，二氧化硅上八面体和四面体 Zn _ads的 XANES 光谱足以进行定量识别。这些结果表明，在使用单个 Zn_广告通过线性组合方法破译天然样品中的 Zn 形态时要谨慎代表特定矿物表面吸附的标准。XANES 光谱特征与先前扩展的 X 射线吸收精细结构 (EXAFS) 衍生的配位环境之间的相关性为二氧化硅样品上的这些 Zn_广告提供了对自然系统中 Zn 形态的洞察，其中 XANES 兼容的 Zn 浓度对于 EXAFS 分析来说太低了。