Facile synthesis of hydroxy-modified MOF-5 for improving the adsorption capacity of hydrogen by lithium doping

A facile synthesis of partially hydroxy-modified MOF-5 and its improved H₂-adsorption capacity by lithium doping are reported. The reaction of Zn(NO₃)₂×6 H₂O with a mixture of terephthalic acid (H₂BDC) and 2-hydroxyterephthalic acid (H ₂BDC-OH) in DMF gave hydroxy-modified MOF-5 (MOF-5-OH-x), in which the molar fraction (x) of BDC-OH^2- was up to 0.54 of the whole ligand. The MOF-5-OH-x frameworks had high BET surface areas (about 3300 m ² g^-1), which were comparable to that of MOF-5. We suggest that the MOF-5-OH-x frameworks are formed by the secondary growth of BDC ^2--rich MOF-5 seed crystals, which are nucleated during the early stage of the reaction. Subsequent Li doping into MOF-5-OH-x results in increased H₂ uptake at 77 K and 0.1 MPa from 1.23 to 1.39 wt. % and an increased isosteric heat of H₂ adsorption from 5.1-4.2 kJ mol ^-1 to 5.5-4.4 kJ mol^-1. Would I Li to you: Li doping into hydroxy-modified MOF-5 (MOF-5-OH-x) results in increased H₂ uptake at 77 K and 0.1 MPa (from 1.23 to 1.39 wt. %) and an increased isosteric heat of H₂ adsorption (from 5.1-4.2 to 5.5-4.4 kJ mol^-1).