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采用平衡分子动力学和巨正则系综蒙特卡洛模拟方法对多孔沸石咪唑酯骨架材料(ZIF-8)中CH4和H2分子的吸附与扩散特性进行了比较研究.结果表明,采用柔性力场能够很好地复制ZIF-8在不同压力或温度条件下的晶体结构,也能准确地计算不同温度下CH4和H2分子在ZIF-8中的扩散系数,特别是高温下CH4分子因能够摆脱ZIF-8骨架笼口的空间限制而使其扩散系数出现大幅提升.同时,该力场也能粗略地模拟CH4和H2分子在ZIF-8中的等温吸附曲线,通过自编程序得到吸附和扩散平衡时CH4和H2分子在ZIF-8单元晶胞内的几率密度分布数据,并利用VMD软件可视化.结果显示CH4和H2分子在ZIF-8中的优先吸附位置均在大孔中心靠近咪唑环的区域,但CH4分子的优先吸附位置有两个不同层次,而H2分子的优先吸附位置只有一个层次,说明CH4和H2分子在ZIF-8中存在着不同的吸附机理.
Adsorption and diffusion characteristics of CH4 and H2 molecules in porous zeolite imidazole ester framework material (ZIF-8) were studied by equilibrium molecular dynamics and macrocontact monte carlo simulation.The results show that the use of flexible force field can It can well duplicate the crystal structure of ZIF-8 under different pressure or temperature conditions, and accurately calculate the diffusion coefficient of CH4 and H2 molecules in ZIF-8 under different temperatures. In particular, CH4 molecules can get rid of ZIF- 8 skeleton cage mouth and its diffusion coefficient greatly increased the same time, the force field can roughly simulate the adsorption isotherm of CH4 and H2 molecules in the ZIF-8 curve, obtained by the self-programmed adsorption and diffusion equilibrium CH4 and H2 molecules in the ZIF-8 cell unit cell density data and visualization using VMD software.The results show that the preferential adsorption position of CH4 and H2 molecules in ZIF-8 are in the center of the big hole near the imidazole ring region, However, the preferential adsorption sites of CH4 have two different levels, while the preferential adsorption sites of H2 have only one level, indicating that there are different adsorption mechanisms of CH4 and H2 in ZIF-8.