Synthesis and formation mechanism of textured MOF-5

Abstract

Textured and house-of-card structures develop on the surfaces of cubic MOF-5 crystals. The formation mechanism of these novel constructions are investigated based on characterisation of the intermediate specimens with different reaction time intervals using scanning and transmission electron microscopies. It is found that the growth of MOF-5 cubic crystals does not follow the classical route. MOF-5 nanocrystallites initially aggregate to form large polycrystalline cubes, followed by surface re-arrangement of the nanocrystallites into a textured structure consisting of nanowires lying along the [100], [010], [110] and [11 ̅0] zone axes, if the face of the cube is defined to be (001). Further crystal growth leads to a house-of-cards structure constructed by interpenetrated nanoplates with their shortest axis parallel to [110] and [11 ̅0] axes. Evidence of a reversed crystal growth process is also observed. MOF-5 cubes with a single crystal-like appearance are achieved with extended reaction times despite their hidden three tier structure containing varying porosities hidden underneath.