Synthesis And Adsorptive Separation Performances Of ZIF-67 And ZIF-69

As a new sub-family of porous metal-organic frameworks?MOFs?,zeolitic imidazolate frameworks?ZIFs?not only have high specific surface area and tunable pore geometry but also possess special thermal stability and chemical stability,especially can be stable in water.Therefore,ZIFs have great potential applications in gas storage and separation,etc.In this paper,the preparation,characterization and adsorption properties of ZIF-67 and ZIF-69 were studied.The main work and results are as follows:?1?ZIF-67 crystals were synthesized by copolymerization of Co²⁺ with 2-methylimidazole links via solvothermal method at room temperature.The effects of Co²⁺ source,the order of mixed reaction chemicals on the morphology were investigated via single-factor experiments.The samples were systematically characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,thermal gravimetric analysis?TG?.The optimum synthetic conditions are as follows: Co?NO3?2·6H2O and m Im dissolved in methanol with Co²⁺/m Im molar ratio of 8.Under the optimum conditions,ZIF-67 with the rules of rhombic dodecahedron was obtained and the crystal diameters are around 200 nm.?2?The adsorption capacity of phenol on ZIF-67 in aqueous solution was studied by the static adsorption experiments,and the adsorption isotherms of the adsorption of phenol on ZIF-67 were studied with Langmuir isotherm equation.The effects of temperature,pH value,initial concentration of phenol were examined.The optimum adsorptive conditions are as follows: adsorption time 2 h,pH value of 9.0 and adsorption temperature of 298 K.And the adsorption isotherms agreed well to the Langmuir adsorption isotherms,which suggests that monolayer adsorption plays a major role.?3?ZIF-69 crystals were synthesized by copolymerization of Zn²⁺ with 2-nitroimidazole and 5-chlorobenzinidazole links via solvothermal method at room temperature.The effects of temperature,concentration and the order of mixed reaction chemicals on the morphology were investigated via single-factor experiments.The samples were systematically characterized by XRD and SEM.The optimum synthetic conditions are as follows: Zn²⁺ was added dropwise into the mixtures of cbIm and nIm with concentration of 0.1 mol/L at room temperature.Under the optimum conditions,the flat hexagonal prisms with double hexagonal pyramid heads ZIF-69 crystals were obtained and the crystal diameters are around 800 nm.?4?The adsorption capacity of C₂H₆ and C₂H₄ on ZIF-69 were investigated.ZIF-69 exhibited greatly preferential adsorption of C₂H₆ over C₂H₄ and the adsorption capacity of C₂H₆ is 2.2 mmol/g at 100 kPa.The adsorptive selectivity of C₂H₆/C₂H₄ was up to 1.7 at pressure below 100 kPa.The isosteric heats of C₂H₆ and C₂H₄ were about 26 and 23 kJ/mol respectively.