Ustinov Eugene A
Ioffe Physical Technical Institute, 26 Polytechnicheskaya, St. Petersburg 194021, Russia.
Langmuir. 2009 Jul 7;25(13):7450-6. doi: 10.1021/la900369b.
Low-temperature nitrogen adsorption in hexagonal pores and equivalent cylindrical pores is analyzed using nonlocal density functional theory extended to amorphous solids (NLDFT-AS). It is found that, despite significant difference of the density distribution over the cross-section of the pore, the capillary condensation/evaporation pressure is not considerably affected by the pore shape being slightly lower in the case of hexagonal geometry. However, the condensation/evaporation step in the hexagonal pore is slightly larger than that in the equivalent cylindrical pore because in the latter case the pore wall surface area and, hence, the amount adsorbed at pressures below the evaporation pressure are underestimated by 5%. We show that a dimensionless parameter defined as the ratio of the condensation/evaporation step and the upper value of the amount adsorbed at the condensation/evaporation pressure can be used as an additional criterion of the correct choice of the gas-solid molecular parameters along with the dependence of condensation/evaporation pressure on the pore diameter. Application of the criteria to experimental data on nitrogen adsorption on a series of MCM-41 silica at 77 K corroborates some evidence that the capillary condensation occurs at equilibrium conditions.
利用扩展到非晶态固体的非局部密度泛函理论（NLDFT - AS）分析了六方孔和等效圆柱孔中的低温氮吸附。结果发现，尽管孔横截面的密度分布存在显著差异，但毛细凝聚/蒸发压力受孔形状的影响不大，六方几何形状的情况下该压力略低。然而，六方孔中的凝聚/蒸发台阶比等效圆柱孔中的略大，因为在后一种情况下，孔壁表面积以及因此在低于蒸发压力下的吸附量被低估了5%。我们表明，一个无量纲参数定义为凝聚/蒸发台阶与凝聚/蒸发压力下吸附量上限的比值，与凝聚/蒸发压力对孔径的依赖性一起，可以用作正确选择气固分子参数的附加标准。将这些标准应用于77 K下一系列MCM - 41二氧化硅上氮吸附的实验数据，证实了一些关于毛细凝聚在平衡条件下发生的证据。
