Study On Preparation And Gas Separation Of SOD Topological Structure Metal-Organic Framework Membrane

Metal organic frameworks（MOFs）have high specific surface area,regular pore size,chemical adjustability,chemical stability and thermal stability,so it was widely used in gas separation and liquid separation to solve the water pollution and air pollution.MOF membranes as an emerging material based on MOF have attract more attentions in the recent years.However,the poor heterogeneous nucleation during the MOF membrane synthesis is a challenge for obtaining high performance MOF membrane.To solve this problem,a combination of dopamine modification and seed coating was used to prepare a high permeability ZIF-8 membrane（SOD-[Zn（mim）₂]（I-43 m,a=17.012（?）,Hmim=2-methylimidazole,also known as MAF-4））.And using the second growth method to prepare MAF-7 membrane（SOD-[Zn（mtz）₂]（I-43 m,a=16.988（?）,Hmtz=3-methyl-1,2,4-triazole））.The main research contents are as follows:1)In the process of preparing the ZIF-8membrane,the homogeneous nucleation in the precursor solution is too fast,caucusing many defects in the membrane.In this paper,a combination of dopamine support and seed coating is used to induce the heterogeneous nucleation and growth of ZIF-8 crystals on the surface of the support,and the fabricated ZIF-8 membrane with a high permeability.This is mainly due to the abundant functional groups of dopamine,which can chelate metal ions(Zn²⁺)to promote nucleation.In addition,dopamine can also anchor the seed crystals,which can effectively prevent the ZIF-8 crystal nuclei from entering the pores of the support,so that the membrane exhibits lower mass transfer resistance and higher H₂ permeability.The membrane was characterized by Fourier Infrared Spectroscopy（FT-IR）,X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The results showed that the method of combining dopaminergic modification support and seed coating can be used to prepare defect-free ZIF-8 membrane.For the single gas permeation performance,the membrane showed a high hydrogen permeance of 1.8×10^-6 mol·m^-2·s^-1·Pa^-1,and the idea selectivity for H₂/CO_2,H₂/N₂,H₂/CH₄,H₂/C₃H₈ is 4.1,8.5,11.3,294.0,respectively.The permeance of the obtained membrane is about one order of magnitude higher than that of similar substrate supported membrane.2)The adsorptions sites of the MOF material are critical for the CO₂ separation by membrane;hence,MAF-7 membranes were developed to prepare for CO₂separation,due to MAF-7 is isomorphic with ZIF-8 and have more adsorptions sites for CO₂.In this work,seed-induced method was used to synthesis MAF-7 membrane.The effects of synthesis parameters（such as the molar ratio to ligand,p H,synthesis temperature）were investigated in detail to obtain the optimum conditions for the synthesis of MAF-7 membrane.The optimal synthesis parameters were obtained at a synthesis temperature of 298 K for 6 h in the precursor solution(1 Zn²⁺:8 Hmtz:3.3 NH₃·H₂O:4444 H₂O).Thus,the MAF-7 membranes with a better morphology and a thinner film layer were prepared.