Influence of the 2-methylimidazole/zinc nitrate hexahydrate molar ratio on the synthesis of zeolitic imidazolate framework-8 crystals at room temperature

The effect of the 2-methylimidazole (Hmim)/zinc nitrate hexahydrate (Zn) molar ratio on the physicochemical characteristics of the zeolitic imidazolate framework-8 (ZIF-8) was investigated. ZIF-8 crystals were synthesized by mixing Hmim with Zn at room temperature without any additives in methanol solution. It was found that Hmim/Zn molar ratio had significant influence on the crystallinity, yield, particle size and porosity of ZIF-8. The samples synthesized at low Hmim/Zn molar ratio showed a cubic shape, whereas at higher Hmim/Zn ratios truncated rhombic dodecahedron or rhombic dodecahedron morphologies were obtained. The particle size is decreased upon increasing the Hmim/Zn molar ratio. Besides, higher Hmim/Zn molar ratio in a certain range resulted in improving crystallinity, yield, surface area and micropore volume of ZIF-8. The ZIF-8 crystals produced at Hmim/Zn molar ratio of 8 exhibited the best characteristics. The present work provides new insights in relation to the role of Hmim/Zn molar ratio on the synthesis process of ZIF-8.