Micropore Formation of [Zn2(Oxac) (Taz)2]·(H2O)2.5 via CO2 Adsorption

As-synthesized [Zn2(Oxac) (Taz)2]·(H2O)2.5, referred to as ZOTW2.5, was prepared from aqueous methanol solutions of Zn5(CO3)2(OH)6 and two kinds of ligands of 1,2,4-triazole (Taz) and oxalic acid (Oxac) at 453 K for 12 h. The crystal structure was determined by the Rietveld method. As-synthesized ZOTW2.5 was pretreated at 383 K and 1 mPa for tpt h, ZOTWx(tpth). ZOTWx(≥3h) showed a type I adsorption isotherm for N2 at 77 K having a saturation amount (Vs) of 180 mg/g, but that pretreated shortly showed only 1/10 in Vs. CO2 was adsorbed at 303 K in sigmoid on nonporous ZOTWx(≤2h) and in Langmuir-type on ZOTWx(≥3h) to reach the adsorption amount of 120 mg/g at 700 Torr. N2 adsorption on ZOTWx(≤2h)deCO2, degassed after CO2 adsorption on ZOTWx(≤2h), was promoted 5-fold from 180 mg/g on ZOTWx(tpth) and ZOTWx(≥3h)deCO2 up to ca. 1000 mg/g. The interaction of CO2 and H2O molecules in micropores may lead to a new route for micropore formation.