For TEM sample preparation, ZIF-8 powder was dispersed in 2 ml of ethanol solution (70 wt.%) and ultrasonicated for 30 mins to obtain a colloidal solution. The solution was drop-casted on holey carbon (AGS147) and graphene-coated Cu grid purchased from Agar Scientific (AGS179-GO4, suspended monolayer Graphene on TEM grid Quantifoil R2/4).