Studies On The Preparation And Separation Performances Of ZIF-8 And MIL-160 Membranes

MOFs is a novel organic-inorganic hybrid porous material developed in recent years.This kind of material is composed of inorganic metal center and organic functional groups through covalent bond or ionic bond mutual connection,together to build a structured pore structure.With high porosity,specific surface area and excellent chemical stability,MOFs has a broad application prospect in the fields of adsorption,separation,catalysis and sensing.In addition,the organic ligands of metal-organic framework compounds usually contain organic functional groups such as aldehyde group,amino group and carboxyl group,which are easy to be improved or endowed with special properties by chemical modification.In particular,there is no need to use template agent in the synthesis of organic metal frame film,which can avoid the cracks in the process of removing the template agent,so it is expected to break through the bottleneck of traditional molecular sieve film preparation.Therefore,in recent years,the preparation and application of metal-organic framework membrane has become a research hotspot.Zeolite imidazoles metal-organic framework materials?ZIFs?is a relatively new MOFs materials,by divalent metal cations(Zn²⁺,Co²⁺,etc.)and imidazole anion formed through coordination,it not only has the general MOFs materials with high specific surface area and porosity,etc.,also has chemistry stability and thermal stability like traditional zeolite,which is expected to synthesize molecular sieve membrane with excellent performance.Therefore,it has attracted much attention from scholars recently.As a representative ZIFs material,ZIF-8 is composed of Zn ion and methyl imidazole ester.It is a tetrahedral structure with a topological structure of sodalite?SOD?.ZIF-8 has a pore diameter of 0.34nm and a cage diameter of 11.6nm.ZIF-8 is widely used in separation and purification because of its high specific surface area,high stability and small aperture.As a new MOFs material,the Materials of Institute Lavoisier frameworks?MIL?are synthesized from transition metals and lanthanides with binary carboxylic acid or from trivalent metals with vanadium,iron,chromium,aluminum and carboxylic acid.Due to its large specific surface area and good stability,it is an excellent material for synthesizing molecular sieve membranes.In recent years,it has received wide attention.MIL-160 is a special MIL material,which is rarely studied in the present research.It is composed of aluminum and carboxylic acid.The MIL-160 not only has a one-dimensional pore with a diameter of 0.5⁰.6 nm,but also has high hydrothermal and chemical stability.Therefore,the molecular sieve of MIL-160membrane has high application value in the fields of liquid separation and seawater desalination.In this paper,the following three aspects of research work are carried out on the ZIF-8 membrane and MIL-160 membrane materials of metal organic framework.In the first part,we modified the?-Al₂O₃ surface with perfluorosilane,and prepared uniform and dense ZIF-8 film on the modified carrier surface by using the principle of"like grows like".The performance characterization of ZIF-8 membrane was mainly evaluated by the permeability of H₂,CH₄,N₂,CO₂ and C₃H₈single-component gas and the separation performance of the mixed gases of H₂/CO₂,H₂/N₂,H₂/CH₄ and H₂/C₃H₈ with the molar ratio.In the test process,the ZIF-8membrane has excellent hydrogen selective permeability.At 200?,1 bar,under the condition of H₂/CO₂,H₂/N₂ and H₂/CH₄ and H₂/C₃H₈ separation factor were15.8,22.6,40.6 and 549.3.In addition,the separation performance of ZIF-8membrane almost remains unchanged and has good stability in the long-term test at different temperatures and pressures.In the second part,we modified the?-Al₂O₃ surface with polydopamine,and MIL-160 membrane was prepared with uniform and dense MIL-160 membrane by utilizing the covalent bond between the amino group,quinone group and other organic functional groups of polydopamine and MIL-160 to promote the nucleation and growth of MIL-160 membrane on the substrate surface.The characterization of MIL-160 films was evaluated by the osmotic vaporization of pure o-xylene,p-xylene,m-xylene and o-xylene at different temperatures.Because MIL-160 membrane has special pore size,it shows high separation performance in the process of pervaporation.At 75?,such as the mole ratio of o-xylene separation factor is 38.5,and after a long time test,MIL-160 membrane separation performance almost remain the same,has a good stability.In the third part,because of the pore size of MIL-160 membrane is exactly between water molecule and hydrated ion,this part will study its seawater desalination performance.We used the pervaporation device to study the water permeability and the ion repulsion rate at different temperatures and different raw liquid concentrations.It was found that the ion repulsion rate of MIL-160 film remained at a higher level?99.8%or more?when the seawater concentration increased,which further confirmed that MIL-160 film had a higher desalination performance.After a long time test,the desalting rate of MIL-160 film can be maintained at a high level,with high thermal stability and hydrothermal stability.