Study On Preparation And Performance Of Gas Separation Composite Membranes Based On Carbon Nanomaterial Interlayer

In recent years,environmental problems caused by excessive CO₂ emissions have greatly affected human life,and the continuous growth of carbon emissions worldwide has highlighted that the global goal of zero carbon emissions is still facing huge challenges.Membrane technology plays an increasingly important role in CO₂ capture due to its low expense,ease of operation and environmental compatibility.Among them,the mixed matrix membrane（MMMs）is expected to break through the"trade-off"limitation and achieve efficient gas separation.But the challenge is to reduce the thickness while maintaining the integrity of the selective layer to avoid defects.By introducing an intermediate layer between the selective layer and the supporting membrane during the interfacial polymerization（IP）process,the distribution of nanofillers can be controlled,and the membrane thickness can be effectively reduced.The intermediate layer can optimize the chemical properties of the IP support membrane,significantly affect the formation of the separation layer,help to form an ultra-thin,defect-free selective layer,and enhance the structural stability of the composite membrane.Therefore,this paper selects graphene oxide（GO）and graphene quantum dots（GQDs）as the intermediate layer,and uses interfacial polymerization to prepare interlayered-thin film nanocomposite（i-TFN）membrane,aiming to study the influence of nano-interlayer on the composite membrane structure and the relationship between the microstructure of the composite membrane and the gas separation performance.In the study of composite membranes based on GO interlayer gas separation,a polyamide（PA）composite membrane was first prepared,and the influence of process parameters such as water phase monomer and concentration,oil phase monomer concentration and reaction time on membrane performance and structure was explored.Then selectβ-cyclodextrin（β-CD）as water phase monomer and TMC as oil phase monomer to prepare polyester（PAR）membrane.The GO intermediate layer was introduced to prepare GO/PA and GO/PAR i-TFN membranes,and the effect of GO deposition on the gas separation performance of i-TFN membranes was investigated.The results show that the chemical structure of PA and PAR membranes are significantly different due to the different effects between the aqueous monomer and the GO intermediate layer.Comprehensive comparison of the separation performance of the two shows that the GO/PAR membrane has the best separation effect and CO₂ permeation was 126.3 GPU,and the CO₂/N₂ selectivity was 15.2.In order to further improve the performance of the gas separation composite membrane,this paper selected zero-dimensional nanomaterials GQDs and aminated graphene quantum dots（N-GQDs）with similar characteristics as GO as the intermediate layer.The effects of nanomaterials with different structures and the deposition amount of nanomaterials on the structure and performance of i-TFN membranes were studied.GQDs and N-GQDs were synthesized by the"bottom-up method",and then used as the intermediate layer,andβ-CD and TMC as the water and oil phase monomers to prepare i-TFN membranes.The research results show that the selective layer of N-GQDs/PAR i-TFN membrae was divided into three layers,the surface layer isβ-CD,N-GQD and TMC react together,the middle layer only hasβ-CD-TMC membrane,and the bottom layer is N-GQDs layer.The comprehensive effect of the selective layer has significantly improved the separation effect,the CO₂ permeation flux increased to 174.5 GPU,and the CO₂/N₂selectivity increased to 23.3.This work proposes a method to effectively improve the membrane performance through the action of the nanomaterial intermediate layer on the structure of the composite membrane,and clarifies the connection between the i-TFN membrane structure and the gas separation performance,which will inspire other nanomaterials to explore Intermediate layer for gas separation.This is of great significance to the preparation of thin-film nanocomposites.