A series of four novel alkaline earth metal-organic frameworks constructed of Ca(ii), Sr(ii), Ba(ii) ions and tetrahedral MTB linker: structural diversity, stability study and low/high-pressure gas adsorption properties

摘要

A series of four novel microporous alkaline earth metal-organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca-4(mu(8)-MTB)(2)]center dot 2DMF center dot 4H(2)O}(n)(UPJS-6), {[Ca-4(mu(4)-O)(mu(8)-MTB)(3/2)(H2O)(4)]center dot 4DMF center dot 4H(2)O}(n)(UPJS-7), {[Sr-3(mu(7)-MTB)(3/2)]center dot 4DMF center dot 7H(2)O}(n)(UPJS-8) and {[Ba-3(mu(7)-MTB)(3/2)(H2O)(6)]center dot 2DMF center dot 4H(2)O}(n)(UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m(2)g(-1)(N-2)/126 m(2)g(-1)(Ar) forUPJS-7 '', 320 m(2)g(-1)(N-2)/358 m(2)g(-1)(Ar) forUPJS-9 '' andUPJS-8 '' adsorbs only a limited amount of N(2)and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 degrees C and 1 atm, and 16.4-13.5 wt% at 30 degrees C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0-2.9 wt% of CH(4)at 30 degrees C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7-1.8 wt% at -196 degrees C and 800 Torr among MTB containing MOFs.