Peng Bo, Yu Yang-Xin
Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China.
Langmuir. 2008 Nov 4;24(21):12431-9. doi: 10.1021/la8024099. Epub 2008 Oct 8.
A density functional theory (DFT) constructed from the modified fundamental-measure theory and the modified Benedict-Webb-Rubin equation of state is presented. The Helmholtz free energy functional due to attractive interaction is expressed as a functional of attractive weighted-density in which the weight function is a mean-field-like type. An obvious advantage of the present theory is that it reproduces accurate bulk properties such as chemical potential, bulk pressure, vapor-liquid interfacial tension, and so forth when compared with molecular simulations and experiments with the same set of molecular parameters. Capabilities of the present DFT are demonstrated by its applicability to adsorption of argon and nitrogen on, respectively, a model cylindrical pore and mesoporous MCM-41 materials. Comparison of the theoretical results of argon in the model cylindrical pore with those from the newly published molecular simulations indicates that the present DFT predicts accurate average densities in the pore, slightly overestimates the pore pressure, and correctly describes the effect of the fluid-pore wall interaction on average densities and pressures in the pore. Application to adsorption of nitrogen on MCM-41 at 77.4 K shows that the present DFT predicts density profiles and adsorption isotherms in good agreement with those from molecular simulations and experiments. In contrast, the hysteresis loop of adsorption calculated from the mean-field theory shifts toward the low pressure region because a low bulk saturated pressure is produced from the mean-field equation of state. The present DFT offers a good way to describe the adsorption isotherms of porous materials as a function of temperature and pressure.
本文提出了一种基于修正的基本度量理论和修正的Benedict-Webb-Rubin状态方程构建的密度泛函理论（DFT）。由吸引相互作用产生的亥姆霍兹自由能泛函被表示为吸引加权密度的泛函，其中权重函数是一种类似平均场的类型。与具有相同分子参数集的分子模拟和实验相比，本理论的一个明显优点是它能再现诸如化学势、体压力、气液界面张力等准确的体性质。通过将本DFT分别应用于氩气和氮气在模型圆柱形孔和介孔MCM-41材料上的吸附，展示了其能力。将模型圆柱形孔中氩气的理论结果与新发表的分子模拟结果进行比较表明，本DFT预测了孔内准确的平均密度，略微高估了孔压力，并正确描述了流体-孔壁相互作用对孔内平均密度和压力的影响。在77.4 K下将其应用于氮气在MCM-41上的吸附表明，本DFT预测的密度分布和吸附等温线与分子模拟和实验结果吻合良好。相比之下，由平均场理论计算的吸附滞后环向低压区域移动，因为平均场状态方程产生了较低的体饱和压力。本DFT提供了一种很好的方法来描述多孔材料的吸附等温线随温度和压力的变化。
