Eller Johannes, Gross Joachim
Institute of Thermodynamics and Thermal Process Engineering, University of Stuttgart, Pfaffenwaldring 9, 70569 Stuttgart, Germany.
Langmuir. 2021 Mar 30;37(12):3538-3549. doi: 10.1021/acs.langmuir.0c03287. Epub 2021 Mar 16.
This study analyzes the adsorption behavior in two-dimensional heterogeneous slit pores using nonlocal density functional theory based on the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state. Both chemical heterogeneity and surface roughness on small atomistic scales are investigated. The solid structure is considered as individual solid interaction sites whereby chemical heterogeneity is introduced through the presence of different solid-fluid sites and molecular roughness by varying the position of the interaction sites in the first solid layers. The effect of both forms of heterogeneity on the adsorption behavior is assessed individually. Effective one-dimensional solid-fluid potentials provide a way to reduce the dimensionality and computational demand of the density functional theory (DFT) calculations. We determine one-dimensional free-energy-averaged (FEA) solid-fluid potentials of methane and -butane in the low-density limit for solid systems with molecular roughness and chemical heterogeneity. Using this effective one-dimensional solid-fluid potential at any density, we find excellent agreement of adsorption isotherms for both solid descriptions in systems with homogeneous slit pores. Subcritical adsorption isotherms of -butane in slit pores with surface roughness show deviations at higher pressures due to the formation of fluid layers in the one-dimensional FEA potential. Chemical heterogeneity introduces a shift of the capillary condensation pressure below the saturation pressure of the bulk liquid, which is well described by the free-energy-averaged system.
本研究基于微扰链统计缔合流体理论（PC-SAFT）状态方程，采用非局部密度泛函理论分析二维非均匀狭缝孔中的吸附行为。研究了小原子尺度上的化学非均匀性和表面粗糙度。固体结构被视为单个固体相互作用位点，通过不同的固液位点引入化学非均匀性，并通过改变第一层固体中相互作用位点的位置引入分子粗糙度。分别评估了两种非均匀性形式对吸附行为的影响。有效的一维固液势提供了一种降低密度泛函理论（DFT）计算的维度和计算需求的方法。我们确定了具有分子粗糙度和化学非均匀性的固体系统在低密度极限下甲烷和丁烷的一维自由能平均（FEA）固液势。在任何密度下使用这种有效的一维固液势，我们发现在均匀狭缝孔系统中，两种固体描述的吸附等温线都具有极好的一致性。具有表面粗糙度的狭缝孔中丁烷的亚临界吸附等温线在较高压力下显示出偏差，这是由于在一维FEA势中形成了流体层。化学非均匀性使毛细管冷凝压力低于本体液体的饱和压力，这可以通过自由能平均系统很好地描述。
