Synthesis And Properties Of Zeolitic Imidazolate Frameworks

Zeolitic Imidazolate Frameworks (ZIFs) are a novel class of Metal-Organic Frameworks (MOFs), ZIF has the common advantages of zeolites and MOFs, such as high specific surface area, high crystallinity, excellent thermal and chemical stability. This makes ZIFs material have been widely used in catalysis, separation and sensors.In this paper, ZIF-67crystals have been successfully prepared from Co2+and Hmim under hydrothermal and room temperature,respectively. The products were characterized by powder X-ray diffraction, scanning electron microscope andN2 sorption.The influence of Hmim:Co2+ molar ratio, the different cobalt salt and reaction time were investigated. According to datum of PXRD and SEM, small-sized crystals were obtained from cobalt nitrate and cobalt chloride, larger-sized crystals were obtained from cobalt sulfate and cobalt acetate, the BET surface area of the product is high to 1395m2g-1.Under hydrothermal conditions, the product ZIF-67 transformed to dia (Co) structure as increasing the reaction time.This article also investigated the influence of Hmim:Co2+ molar ratio, the different cobalt salt and different additive on the size and morphology of ZIF-67synthesized at room temperature. Using cobalt sulfate and cobalt acetate as cobalt sources, ZIF-67 were successfully synthesized at the Hmim:Co2+ molar ratio of 10, the yield of the product is as high as 95%. Alkaline additive is conducive to remove the protons of 2-methylimidazole and accelerate the coordination reaction between metal cobalt and imidazole, tend to form smaller crystals.Compared the two synthesis methods, the reactants dissolved more fully under hydrothermal condition, the crystals show more regular and uniform with a higher specific surface area. Experiments show that the reaction conditions is important for the product. Therefore, we can control the size and morphology of the crystal by changing the reaction conditions.