分子动力学模拟不同类型MOFs材料对NO2气体扩散影响

Molecular Dynamic Simulation on Effects of MOFs Type on NO_2 Diffusivity

利用分子动力学模拟考察了不同浓度条件下NO_2气体在金属有机骨架材料(MOFs)中的自扩散速率,并讨论了气体自扩散速率与材料结构之间的关系。研究结果表明NO_2气体在IRMOF系列材料、具有开放金属位点的MOFs材料和ZIF系列材料中的自扩散系数随着气体浓度增加先升高后降低;在MIL系列材料中的自扩散系数仅随着气体浓度增加而降低。其扩散性能主要受材料最小孔径和孔隙率影响,在同系列材料中最小孔径和孔隙率越大,NO_2气体的自扩散系数越大。其中NO_2气体在IRMOF-9、Mg MOF-74、ZIF-3、MIL-47和MIL-53Crht等材料中均具有较好扩散性能。通过气体分子在材料中的径向分布函数图、模拟轨迹等探讨了气体在MOFs材料中的扩散机理。研究发现MOFs材料金属簇吸附性能的强弱影响NO_2气体随浓度变化的自扩散系数曲线。同时研究了无限稀释条件下NO_2气体在MOFs材料中的自扩散系数D(0),从而获得NO_2在MOFs材料中的活化能。

NO2 self-diffusivity in metal-organic frameworks（MOFs） was studied via molecular dynamics（MD） simulation under different molecular concentrations, and effects of material geometry was analyzed. The results show that NO2 self-diffusivity increases first and then decreases with the increase of NO2 concentration in IRMOF, open-metal sites and ZIF MOFs, and it decreases linearly with the increase of NO2 concentration in MIL MOFs. The self-diffusivity behaviors are mainly affected by pore limiting diameter and void fraction of MOFs. Higher self-diffusivities of NO2 were obtained in MOFs with larger pore limiting diameters and void fractions. IRMOF-9, Mg MOF-74, ZIF-3, MIL-47 and MIL-53 Crht showed good diffusion performance of NO2 gas. Diffusion mechanism was studied by radial distribution functions and MD trajectory of NO2 gas in MOFs. The results show that self-diffusion coefficients of NO2 gas are affected by the interaction of metal cluster of MOFs and NO2 molecule. Activation energies of NO2 in MOFs are obtained through fitting simulated self-diffusivities at infinite dilution D（0） at various temperatures using Arrhenius equation.