Layered clay materials have been used to incorporate transition metal (TM) contaminants. Based on first-principles calculations, we have examined the energetic stability and the electronic properties due to the incorporation of Cd and Hg in layered clay materials, kaolinite (KAO) and pyrophyllite (PYR). The TM can be (i) adsorbed on the clay surface as well as (ii) intercalated between the clay layers. For the intercalated case, the contaminant incorporation rate can be optimized by controlling the interlayer spacing of the clay, namely, pillared clays. Our total energy results reveal that the incorporation of the TMs can be maximized through a suitable tuning of vertical distance between the clay layers. Based on the calculated TM/clay binding energies and the Langmuir absorption model, we estimate the concentrations of the TMs. Further kinetic properties have been examined by calculating the activation energies, where we found energy barriers of $\sim$20 and $\sim$130 meV for adsorbed and intercalated cases, respectively. The adsorption and intercalation of ionized TM adatoms were also considered within the deprotonated KAO surface. This also leads to an optimal interlayer distance which maximizes the TM incorporation rate. By mapping the total charge transfers at the TM/clay interface, we identify a net electronic charge transfer from the TM adatoms to the topmost clay surface layer. The effect of such a charge transfer on the electronic structure of the clay (host) has been examined through a set of X-ray absorption near edge structure (XANES) simulations, characterizing the changes of the XANES spectra upon the presence of the contaminants. Finally, for the pillared clays, we quantify the Cd and Hg K-edge energy shifts of the TMs as a function of the interlayer distance between the clay layers and the Al K-edge spectra for the pristine and pillared clays.

中文翻译：

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保留吸附和嵌入铝硅酸盐粘土中的Cd和Hg污染物：第一个原理研究

层状粘土材料已用于掺入过渡金属（TM）污染物。基于第一性原理计算，我们检查了由于在层状粘土材料，高岭石（KAO）和叶蜡石（PYR）中掺入Cd和Hg而引起的能量稳定性和电子性能。TM可以被（i）吸附在粘土表面上以及（ii）插入在粘土层之间。对于插层情况，可以通过控制粘土（即带柱状粘土）的层间间距来优化污染物的掺入率。我们的总能量结果表明，可以通过适当调整粘土层之间的垂直距离来最大程度地提高TM的掺入量。基于计算的TM /粘土结合能和Langmuir吸收模型，我们估计TMs的浓度。$〜$20和 $〜$吸附和插入的情况分别为130 meV。还考虑了在去质子化的KAO表面内离子化TM吸附原子的吸附和嵌入。这还导致了最佳的层间距离，该距离使TM掺入率最大化。通过映射TM /粘土界面处的总电荷转移，我们确定了从TM吸附原子到最顶层粘土表面层的净电子电荷转移。已通过一组X射线吸收近边缘结构（XANES）模拟检查了这种电荷转移对粘土（主体）电子结构的影响，表征了污染物存在时XANES光谱的变化。最后，对于柱状粘土，