Preparation Of MOFs-based Hybrid Membranes And Their Gas Separation Properties

Compared with other traditional separation methods,membrane separation has the characteristics of energy saving,efficiency and environmental friendship.By combining the advantage of organic and inorganic materials,hybrid membranes,to a certain extent,make up for the weak mechanical strength and terrible high temperature resistance of organic materials and brittleness and poor plasticity of inorganic materials,which have attracted great attentions of researchers.Metal-organic frameworks?MOFs?,as a new type of porous materials,have the advantage of unique skeleton structures,ultra high specific surface area and porosity with broad application prospects in the synthesis of hybrid membrane.Preparation hybrid membranes on the tube is much more difficult than wiping films on the flat due to appearing pinholes and defects beyond control in the film-forming process,but more suitable for the transmission of gas with large loading density.Therefore,researching the preparation of MOFs-based hybrid membranes has great academic value and prospect of industrial application.In this thesis,three common and stable MOFs,CAU-1,NH₂-MIL-53?Al?and ZIF-8,were selected as the research objects,which were doped into organosilica and polyimide.We have discussed the preparation methods of these two kinds of hybrid membranes and their gas separation properties.The details are as follows:?1?By changing the ratio of the solute and the solvent,the synthesis of CAU-1under different concentration conditions were studied.It was found that the size of products was smaller under lower concentration,along with the better gas adsorption performance and selectivity.ZIF-8 and NH₂-MIL-53?Al?with the size of 50⁷0 nm were prepared by the method of room-temperature and solvothermal synthesis,respectively.The results showed that the products had uniform size,high crystallinity and excellent CO₂ adsorption selectivity.?2?Nanoscale MOFs/organosilica hybrid membranes on tubular ceramic substrate were prepared by two-step method.A very thin and compact MOFs/organosilica hybrid nanolayer can be readily formed on the tubular ceramic substrate through the hot-coating followed by calcination processes in a controllable manner.The unique nature of organosilica network has not only enabled us to prepare ultrathin MOF/organosilica membranes less than 150 nm,but also to optimize both peameance and selectivity for their gas separations simultaneously.The as-prepared CAU-1/organosilica membrane has the highest permeance of H₂,which is up to1.47×10^-6 mol?m^-2?s^-1?Pa^-1.ZIF-8/organosilica membrane exhibits excellent ideal separation factors of 30.9 and 35.0 for H₂/N₂ and H₂/CH₄.The ideal separation factors for CO₂/N₂ and CO₂/CH₄ on NH₂-MIL-53?Al?/organosilica membrane are 18.9 and23.2,respectively.?3?MOFs/PI hybrid membranes were prepared on tubular ceramic substrate through simplified modification with organosilica sol and dip-coating MOFs/PI mixture followed by drying step by step.We have discussed the effect of polymer concentration,MOFs loading,pressure,temperature and kinds of MOFs on the gas separation properties.We found that the hybrid membrane with 20%loading of CAU-1 showed very high H₂ permeation rate of 3.09×10^-8 mol?m^-2?s^-1?Pa^-1 and H₂/CO₂ ideal selectivity of 32.8 at room temperature and pressure difference of 0.2MPa.MOFs-based hybrid membranes on tubular ceramic substrate prepared in this thesis have maintained excellent gas permeability and separation performance instead of showing obvious weakness.At the same time,the preparation method is simple,time-saving and mind,providing us a new strategy for studying membrane separation and also possessing potential commercial applications.