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 H 2 ‐adsorption capacity by lithium doping are reported. The reaction of Zn(NO 3 ) 2 ⋅ 6 H 2 O with a mixture of terephthalic acid (H 2 BDC) and 2‐hydroxyterephthalic acid (H 2 BDC‐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 H 2 uptake at 77 K and 0.1 MPa from 1.23 to 1.39 wt. % and an increased isosteric heat of H 2 adsorption from 5.1–4.2 kJ mol −1 to 5.5–4.4 kJ mol −1 .