Construction And Modification CO₂ Transport Channels In Membranes For Enhanced Gas Sepa-ration Performance

Carbon capture technology is the key to energy gas purification and mitigation of greenhouse effect.The membrane separation technology shows a good prospect in the CO₂ separation field due to its advantages of low energy consumption and environmen-tal friendliness.Aiming at enhancing CO₂ separation performance,CO₂ separation membranes have been prepared using covalent organic framework（COF）and two-di-mensional nanomaterial vermiculite（VMT）as building blocks,constructing gas mo-lecular transport channels and modification,regulating the physical and chemical mi-croenvironment to realize the integration of molecular sieve and dissolution-diffusion-reaction multi-selection mechanisms,and to improve the separation performance of the membranes significantly.The details are as follows:Ionic liquid（IL）modified pore channels of COF and enhanced separation perfor-mance of membranes:Based on the regular pore structure and organic properties of COFs,the IL@COF-300/Pebax membranes are fabricated by hybrid method with COF-300 modified by ionic liquid（IL）as the building blocks,and constructing CO₂ transport channels in Pebax matrix.The pore size of COF-300 decreases,improving the diffusion selectivity of CO₂ and CH₄.Moreover,IL affords strong affinity toward CO₂ to improve the solubility selectivity.The IL@COF-300/Pebax membrane shows high CO₂ perme-ability of 1601 barrer with CO₂/CH₄ selectivity of 39,which are 209%and 87.5%higher than that of pristine membrane,respectively,surpassing the 2008 Robeson upper bound.Amino acid intercalation of two-dimensional VMT interlaminar channels and sep-aration performance enhancement of membranes:Based on exfoliability and cation ex-changeability of VMT,VMT membranes are fabricated by vacuum-assisted self-assem-bly using VMT nanosheets as the building blocks.Amino acids are introduced into the VMT to regulate the physical and chemical microenvironment of two-dimensional transport channels.The acid-base pairs in amino acids provide carriers for CO₂transport thus strengthen the reaction mechanism of membranes.The amino acids en-large the interlayer spacing of VMT membranes and strengthen the diffusion mecha-nism.The Arg-VMT membrane shows high CO₂ permeance of 330 GPU with CO₂/CH₄selectivity of 32.1,which are 49%and 105%higher than that of VMT membrane,re-spectively.In addition,the Arg-VMT membrane exhibit good long-term operation stability.Inorganic acid etched two-dimensional VMT laminate channels andseparation performance enhancement of membranes:Based on the etchability of VMT,porous vermiculite（HVMT）nanosheets are prepared by HCl etching,and HVMT membranes are fabricated by vacuum assisted self-assembly method to construct two-dimensional interlaminar channels and laminate channels.The Mg、Al and Ca cations of VMT can be dissolved to form nanopores under appropriate HCl concentration and etching reac-tion conditions,improving the porosity and specificsurface area of VMT,and increas-ing the transport channels on VMT laminates.The amino-rich PEI molecules are intro-duced into HVMT membranes to regulate the channel size and to enhance the diffusion of CO₂.Amino groups afford affinity to CO₂ and thus enhance dissolution and reaction mechanism.The PEI-HVMT membrane shows high CO₂ permeance of 568 GPU with CO₂/CH₄ selectivity of 27.6,which are 157%and 89%higher than that of VMT mem-brane,respectively.In addition,the PEI-HVMT membrane exhibits good long-term operation stability.