多孔金属有机骨架材料储氢性能分子模拟

采用优化的DREIDING力场参数, 通过巨正则系综蒙特卡洛(GCMC)模拟方法对H₂在IRMOF-1、IRMOF-61和IRMOF-62共3种金属有机骨架(MOFs)材料中的吸附平衡性能进行了比较研究. 结果表明, 该力场能够在全压力范围内很好地复制H₂在IRMOF-62材料中的等温吸附曲线; 但对低压下H₂在IRMOF-61中的等温吸附曲线预测出现低估. 与IRMOF-1相比, 具有互穿骨架结构的IRMOF-61和IRMOF-62材料在常温下的储氢能力并无明显提高. 进一步比较77 K时100 kPa、3.0 MPa下H₂在上述MOFs材料中达到吸附平衡时的几率密度分布发现, H₂会优先吸附在Zn₄O骨架附近靠近苯环的位置;对具有互穿结构的MOFs材料而言,由于其孔腔尺寸缩小, 使得H₂优先吸附位区域零散化. 适当长度的有机配体形成的互穿骨架结构能增强与H₂分子之间的相互作用, 具备较高的储氢能力; 而有机配体尺寸过长则会增加骨架结构中H₂吸附死角, 对H₂的吸附能力反而出现下降.

Molecular Simulation on Hydrogen Storage Capacities of Porous Metal Organic Frameworks

The adsorption equilibriumproperties of H₂ molecules in various metal-organic frameworks (MOFs) including IRMOF-61, IRMOF-62, and IRMOF-1 were studied using the grand canonical Monte Carlo (GCMC) simulation method with the optimized parameters obtained using the DREIDING force field. The calculated parameters could exactly reproduce the adsorption isotherms of H₂ molecules in IRMOF-62. However, they may underestimate the adsorption isothermof H₂ molecules in IRMOF-61 at lowpressure. The H₂ storage capacities of IRMOF-61 and IRMOF-62 with interpenetrating frameworks were not significantly higher than that of IRMOF-1 at roomtemperature. H₂ molecules were preferentially adsorbed near Zn₄O units, which were located close to the benzene rings, according to the probability density distribution of H₂ molecules in the above MOFs under adsorption equilibriumconditions at 77 K, 100 kPa, and 3.0 MPa. For the MOFs with interpenetrating frameworks, the area with preferential adsorption sites for H₂ molecules is smaller and more scattered than the MOF without because of their smaller cavity sizes. The organic linker should be of appropriate length to promote the formation of an interpenetrating framework, which can enhance the interaction between the framework and H₂ molecules, and thus improve H₂ storage capacity. If the organic linker is too long, it will decrease the adsorption capacity of the MOF for H₂ because more corners unable to adsorb H₂ are formed.