Preparation And Mass Transfer Mechanism Enhancement Of CO₂ Separation Membranes Based On Graphene Oxide

Efficient and environment-friendly CO₂ membrane separation technology is the key to alleviate the greenhouse effect and realize“carbon neutralization and peak carbon dioxide emissions”.It also shows broad development prospects in the field of separation.Aiming at strengthening the CO₂ separation performance,this study proposed using graphene oxide as the units to construct the inner channels of the membrane.By modifying the two-dimensional nanosheets,a variety of transfer mechanisms were synergistically strengthened,and the relationship between the inner channel structure of the membrane and the mass transfer mechanisms was revealed so as to provide theoretical guidance for the design and the enhanced mass transfer mechanisms of high-performance CO₂ separation membranes.The main research contents are as follows:Phenylalanine modified GO doped with Pebax to prepare mixed matrix membrane and the enhancement of diffusion mechanism:Based on GO two-dimensional lamellar structure and its good dispersibility in aqueous solution,the phe@GO was used as the units to construct mass transfer channels in the membrane and it was also introduced into the Pebax polymer through blending to prepare mixed matrix membrane.After GO was modified by phenylalanine,the distance between GO sheets was significantly increased from 0.69 nm to 1.03 nm and the Pebax segments was destroyed so as to strengthen the CO₂ diffusion mechanism.The prepared phe@GO/Pebax membrane had CO₂ permeability of 212 Barrer and the CO₂/N₂selectivity was up to 59,which were 93%and 68%higher than that of Pebax membrane,respectively.The selectivity of CO₂/CH₄ was also greatly improved to 38.Preparation of amino functionalized GO doped Pebax（NH₂@GO/Pebax）membranes and the enhancement of solution-reaction mechanism:Based on the modifiability of oxygen-containing functional groups on the surface of GO,arg@GO and his@GO were used as structural units to prepare mixed matrix membrane.Amino acids with different isoelectric points were modified in the surface of GO sheets to regulate the physical and chemical microenvironment of membranes.The alkaline sites in amino acids were used as the carriers of CO₂ to strengthen the solution-reaction mechanism of the membrane.In contrast,the arg@GO/Pebax mixed matrix membrane prepared by GO modified with arginine with high isoelectric point had the better performance.The permeability of CO₂ in arg@GO/Pebax membrane reached 169 Barrer,and the selectivity of CO₂/N₂ was 70,which was 54%and 35%higher than that of Pebax membrane,respectively.The permeability of CO₂ in his@GO/Pebax membrane reached 160 Barrer,and the selectivity of CO₂/N₂and CO₂/CH₄was 55 and 16,respectively.Meanwhile,the CO₂ permeability of his@GO/Pebax mixed matrix membrane increased by 39%which is lower than that of arg@GO/Pebax membrane.The preparation of GO modified by coordination porous polymer MOF doped with Pebax to prepare mixed matrix membrane and the enhancement of dissolution-diffusion mechanism:Based on the two-dimensional lamellar structure of GO and the modifiability on its surface,the free amino on the surface of porous coordination polymer MAF-66 was covalently bound with GO,so that MOF was loaded on the surface of GO to maintain good dispersion in the membrane.MAF-66has high CO₂ selective adsorption performance,which can increase the CO₂ solubility coefficient of membrane.At the same time,the larger specific surface area increases the diffusion coefficient of gas molecules in the dense membrane.MAF-66@GO/Pebax membrane has good CO₂/N₂ separation performance with CO₂permeability of 207 Barrer and CO₂/N₂ selectivity of 69.