Design And Synthesis Of Metal-organic Framework Membrane Materials For CO₂ Capture

Membrane separation technology is currently the most promising technology in industrial production.Membrane materials have the characteristics of selective separation of chemical substances.Compared with other traditional separation technologies,membrane separation technology has low energy consumption,less capital,and is environmentally friendly.Solving energy waste and environmental pollution has played a crucial role.Especially for CO2 capture,membrane separation technology has great advantages.As a greenhouse gas,CO2 has a great impact on the natural environment and the global economy,and CO2 is also widely used in industrial production,so it has great market value for CO2 capture.With the research on membrane materials in recent years,MOF membrane materials have also become a research hotspot.MOF membrane has made great progress in gas separation.It has high permeability and selectivity,breaking the balance between selectivity and permeability.At the same time,MOF membranes are widely used in water treatment,pervaporation,and ion transmission.Compared with other porous materials,MOF,as a new type of material,has adjustable line strength,uniform pore size distribution,high specific surface area and unsaturated metal sites.The preparation of MOF membranes for gas separation has great advantages.This work simplifies the preparation process of MOF membranes by designing a variety of MOF membrane preparation methods,improves the separation performance of MOF membranes,and attempts to study the separation mechanism and structural relationship of MOF membranes,and draws the following conclusions:(1)The MOF membrane has great advantages for gas separation,but it still cannot solve the problem of gaps between MOF crystals.The preparation process of MOF membrane is complicated.Hence,we repair the gap between MOF particles through ionic liquid.Ionic liquids are chemically stable and viscous,with a wide liquid range.We loaded the ionic liquid[TETA]L with amino groups into Ni-MOF-74 membrane to prepare a Ni-MOF-74@IL membrane,which is different from the traditional mixed matrix membrane.The separation performance of Ni-MOF-74@[TETA]L membrane depends on Ni-MOF-74.Experimental research shows that at room temperature and 1 bar,the prepared Ni-MOF-74 membrane has high permeability and poor selectivity.After dropping 80 mg ionic liquid,the permeability decreases and the selectivity is greatly improved.When the amount of ionic liquid is less than 80 mg and close to 40 mg,the defects of the MOF membrane cannot be completely repaired,resulting in the Ni-MOF-74@[TETA]L membrane has almost no separation performance for H2/CO2,when the amount of ionic liquid is higher than 80 mg and close to 120 mg,the pores of the MOF are blocked,which leads to a decrease in the separation ability of Ni-MOF-74@[TETA]L membrane for H2/CO2.This shows that a proper amount of ionic liquid can repair the defects of the MOF membrane,which will block a few MOF pores.Therefore,the MOF membrane repaired by ionic liquid cannot fully show the separation performance of the MOF membrane,but it can show an effective prediction of the MOF membrane the separation performance.(2)We develop a method for the preparation of multilayer[TETA]L@MOF membranes by introducing ionic liquids with good separation performance.In the reported literature,few people can successfully prepare two-layer MOF membranes.There are few reports on three-layer membranes for gas separation,and we can easily prepare them.Because the ionic liquid[TETA]L has a strong adsorption capacity for CO2,the multilayer membranes produced have a rare phenomenon of reverse separation.At the same time,as the membrane layer increases,H2/CO2,CH4/CO2 and the separation performance of N2/CO2 is gradually improved.The restricted ionic liquid still maintains a certain degree of fluidity at the microscopic scale,which causes the flux of CO2 to gradually increase with increasing pressure,and the flux returns to the initial value when the pressure is withdrawn.The pressure response can be cycled for several cycles.Finally,the prepare membrane method can also be applied to the preparation of other nano-material films,which is of great significance for the future development of film materials.(3)We exfoliate the two-dimensional metal-organic framework NUS-8 into nanosheets and prepared ultra-thin membrane with the assist of graphene oxide.We adjusted the exfoliate time of NUS-8 to find the best conditions for preparing large and thin nanosheets,and prepared 300-400nm thickness ultra-thin membrane with the assist of graphene oxide.Because MOF has a good gas separation performance,we prepared the NUS-8@GO membrane by layer-by-layer stacking method,which shows good separation performance.At the same time,NUS-8 is relatively simple to synthesize and has good stability,we found that the non-dried NUS-8 particles are easier to exfoliate.This work has a good reference for other two-dimensional MOF materials in the future.