A Multifaceted Study of Methane Adsorption in Metal-Organic Frameworks by Using Three Complementary Techniques

作者：Zhang Yue; Lucier Bryan E G; Fischer Michael; Gan Zhehong; Boyle Paul D; Desveaux Bligh; Huang Yining^*

来源：Chemistry - A European Journal, 2018, 24(31): 7866-7881.

DOI：10.1002/chem.201800424

• adsorption
• density functional calculations
• host-guest systems
• microporous materials
• NMR spectroscopy
• X-ray diffraction

Methane is a promising clean and inexpensive energy alternative to traditional fossil fuels, however, its low volumetric energy density at ambient conditions has made devising viable, efficient methane storage systems very challenging. Metal-organic frameworks (MOFs) are promising candidates for methane storage. In order to improve the methane storage capacity of MOFs, a better understanding of the methane adsorption, mobility, and host-guest interactions within MOFs must be realized. In this study, methane adsorption within alpha-Mg-3(HCO2)(6), alpha-Zn-3(HCO2)(6), SIFSIX-3-Zn, and M-MOF-74 (M=Mg, Zn, Ni, Co) has been comprehensively examined. Single-crystal X-ray diffraction (SCXRD) experiments and DFT calculations of the methane adsorption locations were performed for alpha-Mg-3(HCO2)(6), alpha-Zn-3(HCO2)(6), and SIFSIX-3-Zn. The SCXRD thermal ellipsoids indicate that methane possesses significant mobility at the adsorption sites in each system. H-2 solid-state NMR (SSNMR) experiments targeting deuterated CH3D guests in alpha-Mg-3(HCO2)(6), alpha-Zn-3(HCO2)(6), SIFSIX-3-Zn, and MOF-74 yield an interesting finding: the H-2 SSNMR spectra of methane adsorbed in these MOFs are significantly influenced by the chemical shielding anisotropy in addition to the quadrupolar interaction. The chemical shielding anisotropy contribution is likely due mainly to the nuclear independent chemical shift effect on the MOF surfaces. In addition, the (HSSNMR)-H-2 results and DFT calculations strongly indicate that the methane adsorption strength is linked to the MOF pore size and that dispersive forces are responsible for the methane adsorption in these systems. This work lays a very promising foundation for future studies of methane adsorption locations and dynamics within adsorbent MOF materials.

• 出版日期2018-6-4