Channel Construction,Regulation And Separation Performance Enhancement Of Two-dimensional Materials Based Carbon Capture Membranes

The advanced membrane materials and structures are the core of the membrane process.The precise construction and regulation of membrane channels acts as an important way to optimize the membrane structure and strengthen the mass transfer mechanism,thus realizing the efficient separation process.This study,focusing on the urgent demand of carbon capture in energy and environment,aims at precisely constructing channels of membrane and strengthening the CO₂/CH₄separation performance with strategies of using two-dimensional（2D）materials as building blocks of channels and nanomaterials as intercalators.Finally,the precise construction and regulation of membrane channels at the sub-nanometer scale was successfully achieved,synergistically intensifying the multiple mass transfer mechanisms（solution mechanism,diffusion mechanism and facilitated transport mechanism）in membrane.The structure-property relationship between channel structure and separation performance was revealed.This study is expected to provide a theoretical support for the design and prepare of high-performance CO₂separation membranes.The main research contents are as follows:（1）The dual-2D materials mixed matrix membranes（MMMs）were prepared by physical blending with Pebax as membrane matrix and 2D covalent organic framework（COF）and vermiculite（VMT）as the fillers.Based on the synergistic effect of dual-2D materials,CO₂ transfer channels in MMMs were constructed.By optimizing the proportion of dual-2D materials to regulate the structure of membrane channels,synergistic intensification of the solution-diffusion mechanisms was achieved.The optimized MMMs showed a CO₂ permeability of 1167 Barrer with a CO₂/CH₄selectivity of 36.5.（2）Graphene oxide（GO）-POSS-NH₂ membranes were prepared by vacuum-assisted self-assembly with 2D GO as the channel building blocks and POSS-NH₂,a rigid nanocage,as the versatile intercalator.A quantitative analysis method of the contribution of physical/chemical mechanisms to separation performance was established through intercalating POSS-NH₂into GO to precisely construct and regulate the physical/chemical structure of channels.POSS-NH₂ can precisely regulate the channel size in the range of 4.7（？）-9.1（？）and the amino groups in POSS-NH₂ can facilitate CO₂ transport.By synergistically intensifying the diffusion selective and facilitated transport mechanisms,the optimized membrane showed a CO₂ permeance of 13.03 GPU with a CO₂/CH₄ selectivity of 74.5.（3）GO-NGQDs membranes were prepared by vacuum-assisted self-assembly with 2D GO as the channel building blocks and amino-functionalized graphene quantum dots（NGQDs）as the versatile intercalator.The relationship between the binding energy of groups to CO₂ and selectivity of membrane was established through intercalating functionalized GQDs into GO to precisely construct and regulate the physical/chemical structure of channels.NGQDs can precisely regulate the channel size in the range of 3.9（？）-5（？）and construct CO₂-philic naodomains in membranes.Furthermore,the amino groups in NGQDs can facilitate CO₂ transport.By synergistically intensifying the diffusion selective and facilitated transport mechanisms in membranes,the optimized membrane showed a CO₂ permeance of 151.5 GPU with a CO₂/CH₄ selectivity of 40.5.（4）Ultrathin,defect-free COF-based gas separation membranes were prepared by vacuum-assisted self-assembly with 2D cationic COF（CCOF）and GO as the channel building blocks.The facilitated transport groups were firstly introduced into COF-based membrane through the ionic exchange strategy.By precisely regulating the hierarchical channels（the relative ratio of horizontal channel and vertical channel）to optimize the transfer path of CO₂in membranes.Mover,borate distributed in the CCOFs channel can facilitate the rapid transfer of CO₂.By synergistically intensifying the diffusion selective and facilitated transport mechanisms in membranes the optimized membrane showed a CO₂ permeance of 164.2 GPU with a CO₂/CH₄ selectivity of 27.In conclusion,the physical/chemical structures of membrane channels were precisely constructed and regulated by intercalating nanomaterials into 2D materials,to achieve quantitative analysis of the contribution of physical/chemical mechanisms as well as clarify the structure-property relationship between structure and performance.The study found that the chemical mechanism plays a leading role in the separation of CO₂/CH₄.In the future,we can make further explorations in regulating the chemical microenvironment（functional group types and distribution）of channels,constructing a channel structure with controllable size,uniform carrier distribution and moderate activity,then coordinating and optimizing the physical/chemical mechanism in the membrane to achieve efficient separation of gas molecules.