Preparation And Modification Of ZIF-67 And The Research Of Gas Separation Performance

Metal-organic framework material are porous framework structure materials formed by connecting metal ions or ion clusters and organic ligands through coordination bonds.They have potential application value in adsorption,catalysis,drug loading,and transmission,sense and other fields due to the advantages of large specific surface area,adjustable pore size,and functionalized framework.At the same time,the synthesis conditions for MOFs are mild and the structure are easily modified and designed.These are special qualities of MOFs which are unmatched by traditional inorganic zeolite materials.As a member of zeolite imidazole esters,ZIF-67 is formed by linking metal ions(Co²⁺)and 2-methylimidazole ligand.Because of its high specific surface area and large porosity,ZIF-67 has a good application prospect in gas adsorption and membrane separation fields.In this paper,starting from the crystallization kinetics,ZIF-67 was synthesized by solvothermal method.The effects of different metal ligand ratios,different temperatures,different solvents,and different cobalt metal salts and other conditions on crystal morphology and structure were investigated.The gas adsorption performance test was also carried out,and the results showed that the ZIF-67 crystals with regular morphology and size were obtained under the conditions of the crystallization temperature was 25?,the synthesis time was 12h,the Co²⁺/Hmim was 1:4,the solvent composition was Me OH,the vacuum activation temperature was 150?,and the activation time was 6h.The gas adsorption experiment results showed thatthe ZIF-67 crystal synthesized under this condition has the highest hydrogen adsorption capacity at 77K temperature and 100 k Pa pressure.On the basis of previous studies,ZIF-67 synthesized under the optimal conditions was modified by doping different transition metals Zn²⁺,Mg²⁺,Ni²⁺and doped organic ligands of benzimidazole.The study showed that Zn²⁺participated in the coordination reaction andexisted in the crystal framework.When Mg²⁺and Ni²⁺were doped and modified on ZIF-67,the doping effect of Mg²⁺was significantly better than that of Ni²⁺.When the doping content of Mg²⁺was50%,Mg50-ZIF-67's adsorption capacity of H₂ was the highestwith an adsorption capacity of1.89wt.%.When the doping amount of benzimidazole was 5%,the morphology and size of the synthesized ZIF-67 crystal increased obviously,and the adsorption amount of H₂ was the highest at this time,which was 1.91wt.%.Finally,ZIF-67 membrane was prepared by steam phase transformation on macroporous?-Al2O3 tube.The effects of different solvents,crystallization temperature,crystallization time,different ligand ratios,and different Co inducing sources on the synthesis of ZIF-67 membrane were investigated.It was found that a dense and pure phase ZIF-67 membrane was obtained with synthesis condition of methanol as a solvent,crystallization temperature of 160?and crystallization time of 9 hours.Single gas test showed that permeation rate of H₂ is 1.0×10^-7mol/(m²·s·Pa).The ideal separation selectivities of H₂/CO₂,H₂/N2 and H₂/CH4 are 7.62,11.01and 10.93,respectively.