Size Control and Stability Study of Zeolitic Imidazolate Framework-8 to Prepare Mixed Matrix Membrane

Zeolitic imidazolate framework-8 (ZIF-8) with large particle size possesses significant gas transport resistance, which minimises its efficiency in improving the membrane gas separation performance. Hence, size control of ZIF-8 is of great research interest. In this work, different 2-methylimidazole (Hmim) concentration (molar ratio Zn: Hmim = 1:8 or 1:70) and synthesis solvent (methanol or deionised water) were used to regulate the ZIF-8 particle size. Smaller ZIF-8 particles were produced when the reaction was carried out at high Hmim concentration with short reaction time (≤ 2 min) or when methanol was used as the synthesis solvent. It is postulated that the ZIF-8 particles are more likely to exist in the form of aggregates in the membrane rather than individual particles based on the dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. As particle agglomeration was contributed by both particle drying and instability of ZIF-8 in THF, it was recommended to store the ZIF-8 in methanol suspension prior to usage.