Selective adsorption of ethane and methane on zeolite-like imidazolate frameworks ZIF-8 and ZIF-67: effect of lattice coordination centers

Zeolitic imidazolate frameworks based on 2-methylimidazolate linkers with different particle size (200–1000 nm) and controlled content of Zn²⁺ and Co²⁺ ions have been synthesized by microwave (MW) assisted technique according to original procedures and room-temperature method. The produced materials including monometallic ZIF-8 and ZIF-67 samples, bimetallic ZIF-Zn/Co (or ZIF-8/ZIF-67) system, and “core-shell” ZIF-8@ZIF-67 and ZIF-67@ZIF-8 composites have been studied in the practically relevant process of selective adsorption of ethane and methane (25 °C). The adsorption isotherms for both gases on the obtained ZIF materials were measured in a wide pressure range (1–20 atm) for the first time. For ZIF-67, the isosteric heats of adsorption for both gases were obtained also for the first time. It was found that the nature of the coordination centers in the ZIF frameworks influences their adsorption characteristics. Thus, the obtained materials with Co²⁺ ions show an increased adsorption capacity towards ethane, which exceEDX the capacity measured for the Zn²⁺-based samples, while the highest methane adsorption value is achieved on a “core-shell” ZIF-67@ZIF-8 composite.