Controlling ZIF-67 crystals formation through various cobalt sources in aqueous solution

Zeolitic imidazolate frameworks ZIF-67 were prepared under hydrothermal (120 °C) and non-hydrothermal (room temperature) from various cobalt sources and 2-methylimidazolate (Hmim) in aqueous solution within 30 min. The particle size and morphology were found to be related to the reactivity of the cobalt salt, Hmim/Co2+ molar ratios and experimental condition. Using Co(NO3)2 as cobalt source, small-sized ZIF-67 crystals with agglomeration were formed. For CoCl2, small-sized rhombic dodecahedron were obtained. While large-sized crystals of rhombic dodecahedron structure were obtained from CoSO4 and Co(OAc)2. Under hydrothermal condition, the size of ZIF-67 crystals tended to be more uniform and the morphology were more regular comparing to non-hydrothermal condition. This study provides a simple way to control the size and morphology of ZIF-67 crystals prepared in aqueous solution.