Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91106, USA.
J Phys Chem A. 2010 Oct 14;114(40):10824-33. doi: 10.1021/jp1044139.
We determined the methane (CH(4)) uptake (at 298 K and 1 to 100 bar pressure) for a variety of covalent organic frameworks (COFs), including both two-dimensional (COF-1, COF-5, COF-6, COF-8, and COF-10) and three-dimensional (COF-102, COF-103, COF-105, and COF-108) systems. For all COFs, the CH(4) uptake was predicted from grand canonical Monte Carlo (GCMC) simulations based on force fields (FF) developed to fit accurate quantum mechanics (QM) [second order Møller-Plesset (MP2) perturbation theory using doubly polarized quadruple-ζ (QZVPP) basis sets]. This FF was validated by comparison with the equation of state for CH(4) and by comparison with the experimental uptake isotherms at 298 K (reported here for COF-5 and COF-8), which agrees well (within 2% for 1-100 bar) with the GCMC simulations. From our simulations we have been able to observe, for the first time, multilayer formation coexisting with a pore filling mechanism. The best COF in terms of total volume of CH(4) per unit volume COF absorbent is COF-1, which can store 195 v/v at 298 K and 30 bar, exceeding the U.S. Department of Energy target for CH(4) storage of 180 v/v at 298 K and 35 bar. The best COFs on a delivery amount basis (volume adsorbed from 5 to 100 bar) are COF-102 and COF-103 with values of 230 and 234 v(STP: 298 K, 1.01 bar)/v, respectively, making these promising materials for practical methane storage.
我们测定了多种共价有机骨架（COF）的甲烷（CH4）吸收量（在 298 K 和 1 到 100 巴的压力下），包括二维（COF-1、COF-5、COF-6、COF-8 和 COF-10）和三维（COF-102、COF-103、COF-105 和 COF-108）系统。对于所有 COF，CH4 的吸收量都是根据基于力场（FF）的正则系综蒙特卡罗（GCMC）模拟预测的，这些力场是为拟合准确的量子力学（QM）[二阶 Møller-Plesset（MP2）微扰理论，使用双极化四重ζ（QZVPP）基组]而开发的。该 FF 通过与 CH4 的状态方程进行比较以及与 298 K 时的实验吸收等温线（在此报告 COF-5 和 COF-8 的实验数据）进行比较得到了验证，结果吻合良好（在 1 到 100 巴范围内误差在 2%以内），与 GCMC 模拟结果一致。通过我们的模拟，我们首次能够观察到多层形成与孔填充机制共存的现象。就单位体积 COF 吸收剂的 CH4 总容积而言，COF-1 是最好的 COF，在 298 K 和 30 巴下可以储存 195 v/v，超过了美国能源部 298 K 和 35 巴下 CH4 储存目标的 180 v/v。按输送量（从 5 到 100 巴吸附的体积）计算，COF-102 和 COF-103 的吸附量最好，分别为 230 和 234 v（STP：298 K，1.01 bar）/v，这使得它们成为实用甲烷储存的有前途的材料。
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