A model study of effect of M = Li~+, Na~+, Be~(2+), Mg~(2+)and Al~(3+) ion decoration on hydrogen adsorption of metal-organic framework-5

摘要

The effect of light metal ion decoration of the organic linker in metal-organic framework MOF-5 on its hydrogen adsorption with respect to its hydrogen binding energy (AB.E.) and gravimetric storage capacity is examined theoretically by employing models of the form MC_6H_6:nH_2 where M = Li~+, Na~+, Be~(2+), Mg~(2+), and Al~(3+). A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out. Our results show that the interaction energy (AE) of the metal ion M with the benzene ring, AB.E., and charge transfer (Q_(trans)) from the metal to benzene ring exhibit the same increasing order: Na~+ < Li~+ < Mg~(2+) < Be~(2+) < Al~(3+). Organic linker decoration with the above metal ions strengthened H_2-MOF-5 interactions relative to its pure state. However, amongst these ions only Mg~(2+) ion resulted in AB.E. magnitudes that were optimal for allowing room temper-ature hydrogen storage applications of MOF-5. A much higher gravimetric storage capacity (6.15 wt.% H_2) is also predicted for Mg~(2+)-decorated MOF-5 as compared to both pure MOF-5 and Li~+-decorated MOF-5.