Growth And Gas Permeation Properties Of Hybrid Ultramicroporous Material Membrane

Metal-organic frameworks?MOFs?are composed of metal ions or metal-oxide clusters and organic linkers to form porous materials.Over the past few decades,the structural diversity of MOFs and a wide range of applications have been reported.Hybrid ultramicroporous materials?HUMs?is an important subclass of MOFs.They exhibit remarkable gas sorption properties because of some features:the structure is composed of inorganic anion ligand and organic ligand with metal;the pore size is small and adjustable;the inorganic anion in the pore wall has strong force on the gas,etc.SIFSIX-3-M?M=Cu,Zn,Ni,Co,etc.?materials is subclass of HUMs materials.This subclass,which shows remarkable gas sorption properties at room temperature,has been developed.Metal–organic material membrane fabricated from SIFSIX-3-M would combine several features of HUMs materials,enhancing gas separation performances.SIFSIX-3-M?M=Cu,Zn,Ni,Co,etc.?materials are based on two-dimensional grids which M²⁺ions coordinate with pyrazine,pillared by SiF₆^2-?SIFSIX?ions to form three-dimensional framework.The characteristics of this material is the anion SiF₆^2-on pore surface which has strong physisorption interactions with CO₂,C₂H₂,H₂S and etc.In addition,the prolapse fluorine atoms of SiF₆^2-will limit the aperture size to form the ultramicroporous structure.The pore size of this material is similar to the molecular size of some gases?including N₂,CO₂,CH₄,etc.?,which further strengthens the force with gas molecules.Although SIFSIX-3-M series materials have good selective gas adsorption properties,there are few reports on the use of these materials to fabricate gas separation membranes.In this thesis,two kinds of HUMs,SIFSIX-3-Cu and SIFSIX-3-Ni,were selected to fabricate metal-organic framework membranes.SIFSIX-3-Cu and SIFSIX-3-Ni crystals have the advantage of small pore size and strong force on CO₂,which enables these materials to adsorb gas molecules with large kinetic diameters such as CO₂,facilitates the pass of H₂ with small size and consequently improves their gas separation performance.However,due to their different growth conditions and different adsorption amount and enthalpy of CO₂ of these two materials,the quality of the membrane obtained was different.Through detailed regulation of temperature,concentration,time,solvent and other growth conditions,the growth rules of these two kinds of crystaline materials were obtained.Finally,two kinds of metal-organic framework membranes were successfully prepared and single component gas permeation test was conducted.The preparation of SIFSIX-3-Cu requires CuSiF₆ to provide metal ions and inorganic anionic ligands,but CuSiF₆ is expensive to prepare membrane and difficult to obtain.?NH₄?₂SiF₆ is more economical than CuSiF₆.In this thesis,instead of CuSiF₆,?NH₄?₂SiF₆ was used to prepare SIFSIX-3-Cu membranes on the substrate surface by a new method.Firstly,porous SiO₂ substrate was modified by?NH₄?₂SiF₆and SIFSIX-3-Cu membrane was grown on the substrates directly.By SEM characterization,a dense membrane with a thickness of about 20?m was obtained.Gas permeation tests on SIFSIX-3-Cu membrane show that the membrane has good selectivity.The permeability of each gases is basically unchanged after continuous tests,indicating SIFSIX-3-Cu membrane have good stability.In comparison,SIFSIX-3-Ni has a better stability in moist air.In situ growth method can also be used to control the growth of SIFSIX-3-Ni membrane in the substrate.We also used?NH₄?₂SiF₆to modify porous SiO₂ substrates at first and grew a dense layer of SIFSIX-3-Ni crystals.The growth pattern of the membrane at different temperatures and concentrations were discussed in detail through SEM.The fabrication method in this thesis will provide a new strategy for the preparation of polycrystalline membranes.