Lomba Enrique, Bores Cecilia, Sánchez-Gil Vicente, Noya Eva G
Instituto de Química Física Rocasolano, CSIC, Serrano 119, E-28006 Madrid, Spain.
J Chem Phys. 2015 Oct 28;143(16):164703. doi: 10.1063/1.4934230.
In this work, we explore the ability of an inhomogeneous integral equation approach to provide a full three dimensional description of simple fluids under conditions of confinement in porous media. Explicitly, we will consider the case of argon adsorbed into silicalite-1, silicalite-2, and an all-silica analogue of faujasite, with a porous structure composed of linear (and zig-zag in the case of silicalite-1) channels of 5-8 Å diameter. The equation is based on the three dimensional Ornstein-Zernike approximation proposed by Beglov and Roux [J. Chem. Phys. 103, 360 (1995)] in combination with the use of an approximate fluid-fluid direct correlation function furnished by the replica Ornstein-Zernike equation with a hypernetted chain closure. Comparison with the results of grand canonical Monte Carlo/molecular dynamics simulations evidences that the theory provides an accurate description for the three dimensional density distribution of the adsorbed fluid, both at the level of density profiles and bidimensional density maps across representative sections of the porous material. In the case of very tight confinement (silicalite-1 and silicalite-2), solutions at low temperatures could not be found due to convergence difficulties, but for faujasite, which presents substantially larger channels, temperatures as low as 77 K are accessible to the integral equation. The overall results indicate that the theoretical approximation can be an excellent tool to characterize the microscopic adsorption behavior of porous materials.
在这项工作中，我们探索了一种非均匀积分方程方法在多孔介质受限条件下对简单流体进行完整三维描述的能力。具体而言，我们将考虑氩气吸附到硅沸石 -1、硅沸石 -2 以及八面沸石的全硅类似物中的情况，其多孔结构由直径为 5 - 8 Å 的线性（硅沸石 -1 中为锯齿形）通道组成。该方程基于 Beglov 和 Roux [《化学物理杂志》103, 360 (1995)] 提出的三维奥恩斯坦 - 泽尼克近似，并结合使用由具有超网链闭合的复制奥恩斯坦 - 泽尼克方程提供的近似流体 - 流体直接相关函数。与巨正则蒙特卡罗/分子动力学模拟结果的比较表明，该理论在密度分布曲线以及多孔材料代表性截面的二维密度图层面上，都能对吸附流体的三维密度分布提供准确描述。在非常紧密的受限情况（硅沸石 -1 和硅沸石 -2）下，由于收敛困难无法找到低温下的解，但对于具有明显更大通道的八面沸石，积分方程能够处理低至 77 K 的温度。总体结果表明，该理论近似可以成为表征多孔材料微观吸附行为的出色工具。
