4.6 Article

Density functional theory of adsorption in spherical cavities and pore size characterization of templated nanoporous silicas with cubic and three-dimensional hexagonal structures

期刊

LANGMUIR
卷 18, 期 5, 页码 1550-1560

出版社

AMER CHEMICAL SOC
DOI: 10.1021/la0107594

关键词

-

向作者/读者索取更多资源

Adsorption in spherical cavities is studied by the nonlocal density functional theory (NLDFT). Theoretical results are compared with experimental data on ordered nanoporous materials with cubic Pm3n (SBA-1, HMM-3), cubic Im3m (SBA-16), and 3D hexagonal P6(3)/mmc (SBA-2, SBA-12) cagelike structures. Quantitative comparison shows that capillary condensation of N(2) at 77 Kin sufficiently small cavities (pore diameters 3 < D < 6 nm) occurs reversibly; the equilibrium condensation pressure is determined by the cavity diameter. In the case of hysteretic isotherms on materials with cavity diameters of >ca. 6 nm, the capillary condensation step corresponds to the theoretical limit of stability of the metastable adsorption film. For pores wider than ca. 10 nm, this limit is approximated by the macroscopic Derjaguin-Broekhoff-de Boer equations. Desorption from cavities of >6 nm is controlled by the size of the windows that connect the cavity with the bulk fluid. If the diameter of the window is below ca. 4 rim, desorption occurs via spontaneous cavitation of condensed liquid. We developed a NLDFT method for calculating pore size distributions (PSD) of cavities, the amount of intrawall porosity, and, in combination with X-ray diffraction, the wall thickness in siliceous materials with cagelike pores. We demonstrate that the adsorption method allows one to differentiate between the materials of different morphological symmetry. For regular cagelike structures, the NLDFT results are in remarkably good agreement with the estimates derived from geometrical considerations. In contrast, the conventional Barrett-Joyner-Halenda method of PSD analysis, based on the Kelvin equation, underestimates the pore sizes in cagelike nanopores by up to 100%.

作者

我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。

评论

主要评分

4.6
评分不足

次要评分

新颖性
-
重要性
-
科学严谨性
-
评价这篇论文

推荐

暂无数据
暂无数据