Departament de Quimica, Universitat Autònoma de Barcelona, Bellaterra, Spain.
J Phys Chem A. 2011 Oct 20;115(41):11221-8. doi: 10.1021/jp203988j. Epub 2011 Sep 7.
The adsorption of a single H(2)O and NH(3) molecule on different fully hydroxylated α-quartz, cristobalite, and tridymite surfaces has been studied at the B3LYP level of theory, within a periodic approach using basis sets of polarized triple-ζ quality and accounting for basis set superposition error (BSSE). Fully hydroxylated crystalline silica exhibits SiOH as terminal groups whose distribution and H-bond features depend on both the considered silica polymorph and the crystallographic plane, which gives rise to isolated, H-bond interacting SiOH pairs or infinitely connected H-bond chains. A key point of the present study is to understand how the H-bond features of a dry crystalline silica surface influence its adsorption properties. Results reveal that the silica-adsorbate (H(2)O and NH(3)) interaction energy anticorrelates with the density of SiOH groups at the surface. This counterintuitive observation arises from the fact that pre-existing H-bonds of the dry surface need to be broken to establish new H-bonds between the surface and the adsorbate, which manifests in a sizable energy cost due to surface deformation. A simple method is also proposed to estimate the strength of the pre-existing H-bonds at the dry surfaces, which is shown to anticorrelate with the adsorbate interaction energy, in agreement with the above trends.
采用基于密度泛函理论（B3LYP）的周期性方法，在极化三 ζ 质量基组的基础上，并考虑了基组叠加误差（BSSE），研究了单个 H(2)O 和 NH(3)分子在不同全羟化 α-石英、方石英和鳞石英表面上的吸附情况。全羟化结晶二氧化硅表现出 SiOH 作为末端基团，其分布和氢键特征取决于所考虑的二氧化硅多晶型和晶面，从而产生孤立的、氢键相互作用的 SiOH 对或无限连接的氢键链。本研究的一个关键点是了解干燥结晶二氧化硅表面的氢键特征如何影响其吸附性能。结果表明，二氧化硅-吸附物（H(2)O 和 NH(3))相互作用能与表面上 SiOH 基团的密度呈反相关。这种违反直觉的观察结果源于这样一个事实，即需要打破干燥表面的预先存在的氢键，才能在表面和吸附物之间建立新的氢键，这由于表面变形而表现出相当大的能量成本。还提出了一种简单的方法来估计干燥表面上预先存在的氢键的强度，结果表明氢键强度与吸附物相互作用能呈反相关，这与上述趋势一致。
