Tuning the Adsorption Selectivity of ZIF-8 by Amorphization.

Amorphous metal-organic frameworks (am MOFs) with a partially collapsed structure are a new category of porous hybrid materials. Here, solid-state amorphization of ZIF-8 was achieved by mechanical compression at 0.75 GPa. The compression-induced amorphous ZIF-8 (am ZIF-8) had a collapsed structure, but retained partial porosity. Benefiting from the deformed channel, the resultant am ZIF-8 exhibited preferable adsorption of C3 H6 , resulting in higher thermodynamic adsorption selectivity of C3 H6 /C3 H8 (6.72) than the crystalline counterparts (1.06). Further, am ZIF-8 achieved complete separation of an equimolar C3 H6 /C3 H8 mixture with the first breakthrough of C3 H8 . am ZIF-8 also displayed an enhancement in CO2 /N2 and CO2 /CH4 adsorption selectivities. More importantly, a self-standing am ZIF-8 membrane with boundary-free microstructure was constructed for the first time, and exhibited separation potential for H2 /CH4 , CO2 /N2 , CO2 /CH4 , and C3 H6 /C3 H8 with ideal selectivities of 14.79, 12.83, 16.23, and 2.67, respectively.