The Preparation And Gas Separation Performance Of PEO-based Electrospun Nanofiber Composite Membrane

With the global excessive emission of CO₂ increasing by years,the greenhouse effect of the atmosphere has become increasingly serious,making the research and development of carbon capture related technologies further important.Among the many CO₂ capture methods,the membrane separation method is gaining widespread attention due to its environmental friendliness,compact design,easy maintenance and low cost.The core component of membrane separation technology is the material of membrane.An excellent membrane material needs to have both high CO₂ permeability,high CO₂/N₂ selectivity and good mechanical properties.The current polymer membranes usually have the advantages of large permeability and easy preparation,but their gas permeability and selectivity are difficult to break through the"trade-off"effect limitation.Hybrid membranes prepared by adding organic/inorganic fillers to polymers can improve the CO₂ separation performance of the membranes to a certain extent,but in order to obtain higher CO₂/N₂ selectivity and better mechanical properties,a new membrane structure is urgently needed.Therefore,based on the advantages of electrospun fibers with high specific surface area,high porosity,and easy large-scale preparation,this paper proposes to use small molecule polymers rich in EO functional groups to in situ photopolymerize the fiber gaps,constructing a new kind of fiber interpenetrating network structure and dense CO₂ gas separation membrane,while improving gas permeability,selectivity and mechanical properties.This paper proposes that the PAN fiber mat is first prepared by electrospinning,and ultrafiltration is used to assist small molecules PEGDA and PEGMEA to penetrate into the fiber gaps,and then PEG small molecules are polymerized in situ under ultraviolet light to form a PEO cross-linked network structure to realize the gaps sewing which preparing a dense PEO/PAN nanofiber composite membrane(NFCM).The cross-sectional SEM results of the membrane showed the dense structure of the composite membrane.The results of TGA,DSC,FTIR and XPS showed that PEG was successfully polymerized in the fiber gaps,and the two had good interface compatibility.The effects of PEO cross-linking network density in the membrane and different proportions of PEO filling liquid on the gas separation performance of the membrane were studied.The results show that the 3:7/PAN NFCM membrane has the best CO₂ separation performance.It can maintain the 343 Barrer CO₂ permeability while increasing the selectivity by 27%compared to the pure membrane,and the performance exceeds the Robeson's upper bound line(2008).The increased selectivity mainly comes from electrospun fibers trapped in the membrane through gaps and tortuous gas transmission paths.On the other hand,the fiber forms a"reinforced concrete"structure with the polymer in the membrane,which greatly enhances the mechanical properties of the membrane.The tensile strength at break of3:7/PAN NFCM can reach 3.33 MPa,the elongation at break can reach 25.91%,and the Young's modulus increased to 48.6,corresponding to the same proportion of pure PEO cross-linked membrane increased to 10.4,7.6 and 7.6 times,which is beneficial to practical industrial applications.Since PAN fibers are almost impermeable to gas,in order to further enhance the CO₂permeability of nanofiber composite membranes,this paper proposes to grow ZIF-8nanoparticles on the surface of PAN fibers to enhance the fiber's CO₂ selective adsorption and permeability capabilities.The ZIF-8@PAN nanofiber mat with high ZIF-8 loading was prepared by the in-situ secondary growth method.The influence of different ZIF-8 growth times on the structure and performance of nanofiber mats was explored,and the loading of ZIF-8 can reach up to 59.5 wt%.As the number of growth increases,the crystal structure and chemical structure of ZIF-8 are more obvious and have good thermal stability.The BET results prove that the nanofiber mat exhibits a typical ZIF-8 pore structure and the increase in ZIF-8 load effectively increases the specific surface area,up to 495.49 m² g^-1.The CO₂ adsorption test results show that the CO₂ adsorption capacity increases with the increase of the ZIF-8 loading.Among them,the best performance ZIF-8@PAN-4 NFM can reach 11.57 cm³/g,which makes ZIF-8@PAN nanofiber mats have good CO₂ adsorption performance and CO₂/N₂ separation potential.PEO/ZIF-8@PAN NFCM was prepared by using the above-mentioned high-load ZIF-8@PAN nanofiber mat using PEG in-situ photopolymerization to sew the gaps.SEM,DSC and FTIR results show that ZIF-8 grows uniformly along the fiber,is evenly dispersed in the membrane,and has good interface compatibility with the membrane.TGA results show that the highest content of ZIF-8 in the composite film is as high as 25.5 wt%.The results of CO₂separation of the membrane showed that the CO₂ permeability of the membrane increased with the increase of the number of ZIF-8 growth.Among them,the CO₂ permeability of PEO/ZIF-8@PAN-4 NFCM reaches 129.7 Barrer,which is 33%higher than that of NFCM without ZIF-8,while remains CO₂/N₂ selectivity unchanged basically.The mechanical strength results prove that ZIF-8 on the fiber surface can reinforce the"reinforced concrete"structure of the membrane.Among them,PEO/ZIF-8@PAN-4 NFCM with the best CO₂ permeability has a tensile strength at break of 7.54 MPa,which is 1.17 times higher than that of 10:0/PAN NFCM.