Generation of Amorphous Silica Surfaces with Controlled Roughness
Generation of Amorphous Silica Surfaces with Controlled Roughness
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DOI：
10.1021/acs.jpca.3c04955
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发表时间：
2023-11-08
影响因子：
2.9
通讯作者：
Laird，Brian B.
中科院分区：
文献类型：
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作者：
Nguyen，Nuong P.;Laird，Brian B.
非晶态SiO_2(a-SiO_2)表面，当在功能化表面的活性中心上接枝上特定的金属时，可以作为有用的多相催化剂。从分子模拟的角度来看，一个挑战是建立表面粗糙度可控的a-SiO_2平板模型，以便于研究表面形貌对材料性能的影响。以前的计算方法要么产生相对平坦的表面，要么产生周期性的波纹表面，这些表面不能模拟非晶态二氧化硅材料潜在的表面粗糙度的全部范围。在这项工作中，我们提出了一种新的方法，该方法受界面毛细涨落理论的启发，通过使用解理平面对大块非晶态样品进行解理来产生粗糙的二氧化硅板片，解理平面的傅立叶分量由高斯分布随机产生。可以通过改变表面粗糙度参数α来调节该高斯分布的宽度(以及表面粗糙度)。使用van Beest、Kramer和van Santen(BKS)力场，我们使用不同粗糙度(α)的解理表面和两种不同的系统大小创建了大量的硅片。然后对这些表面进行表征，以确定它们的粗糙度(均方位移)、密度分布和环大小分布。这一分析表明，随着表面粗糙度的增加，表面缺陷(原子配位不足/配位过多和应变环)的浓度更高。为了考察粗糙度对表面反应性的影响，我们使用反应力场ReaxFF重新平衡了这些板材的子集，然后将这些板材暴露在水中，观察表面硅烷醇的形成。我们观察到较粗糙的表面表现出较高的硅醇浓度以及双峰酸度。
Amorphous silica (a-SiO2) surfaces, when grafted with select metals on the active sites of the functionalized surfaces, can act as useful heterogeneous catalysts. From a molecular modeling perspective, one challenge has been generating a-SiO2slab models with controllable surface roughness to facilitate the study of the effect of surface morphology on the material properties. Previous computational methods either generate relatively flat surfaces or periodically corrugated surfaces that do not mimic the full range of potential surface roughness of the amorphous silica material. In this work, we present a new method, inspired by the capillary fluctuation theory of interfaces, in which rough silica slabs are generated by cleaving a bulk amorphous sample using a cleaving plane with Fourier components randomly generated from a Gaussian distribution. The width of this Gaussian distribution (and thus the degree of surface roughness) can be tuned by varying the surface roughness parameter α. Using the van Beest, Kramer, and van Santen (BKS) force field, we create a large number of silica slabs using cleaving surfaces of varying roughness (α) and using two different system sizes. These surfaces are then characterized to determine their roughness (mean-squared displacement), density profile, and ring size distribution. This analysis shows a higher concentration of surface defects (under-/overcoordinated atoms and strained rings) as the surface roughness increases. To examine the effect of the roughness on surface reactivity, we re-equilibriate a subset of these slabs using the reactive force field ReaxFF and then expose the slabs to water and observe the formation of surface silanols. We observe that the rougher surfaces exhibit higher silanol concentrations as well as bimodal acidity.