Preparation And Application Of Two-dimensional Covalent Organic Framework Membrane Materials

Covalent-organic frameworks(COFs)are a new type of crystalline porous materials connected by covalent bonds,with a periodically expanding network structure.Due to its special structural characteristics,COFs are composed of light elements(most of the COFs are composed of C,N,O),large specific surface area,adjustable pore size,and organic connectors that are easy to adjust and cut.The fields of separation and efficient separation of liquid phase macromolecules have broad application prospects.In recent years,independent COF membranes prepared from covalent organic framework materials and composite membranes based on COF have received widespread attention.In particular,the two-dimensional covalent organic framework nanosheets can produce regular ultra-thin COF membranes due to the structural advantages such as large aspect ratio and perfect crystal structure,and have great application potential in separation.To this end,based on the preparation of ultra-thin covalent-organic framework nanosheets(CONs),this paper proposes a variety of membrane manufacturing methods,and synthesizes two-dimensional covalent organic framework membrane materials based Excellent gas separation performance.In view of the difficulties in the current complicated methods of CONs synthesis and the large pore size,this work separately proposed the "bottom-up" and top-down" synthesis strategies,and prepared the ultra-thin CONs-based ultra-thin gas separation membrane.The specific results are as follows:(1)Using a "top-down" synthesis strategy,ultra-thin CTF-1 nanosheets were obtained by liquid phase wet grinding of bulk COF materials and ultrasonic-assisted stripping.Using the "bottom-up" synthesis strategy,ultra-thin TpPa-HSO3 nanosheets were obtained by the direct growth interface polymerization method.And using TEM and AFM characterization methods to study the morphology of nanosheets.(2)Two-dimensional(2D)covalent organic framework(COF)materials can be peeled off into single-layer or oligo-layer nanosheets,and then re-stacked by controlling the re-stacking method and thickness to form ultra-thin membranes.However,the traditional method mainly relies on increasing the thickness(vertical direction control)to achieve high separation selectivity,which still limits the realization of high permeability.In this work,a heating vacuum filtration method that introduces thermal disturbance is proposed,and the COF ultra-thin membrane is prepared by adjusting the horizontal restacking control.Without sacrificing thickness control,the relative displacement of the nanosheets along the carrier surface in the horizontal direction can be optimized.The obtained COF membrane showed high H2 permeability(655.6 GPU)and high H2/CO2 selectivity(43.2).In addition,this method can be extended to other membranes based on two-dimensional(2D)COF nanosheets,which can control the re-stacked microstructure and corresponding characteristics of 2D COF membranes.(3)The separation performance of mixed matrix membranes(MMMs)with ultra-thin CTF-1 nanosheets as fillers for CO2/CH4 and CO2/N2 mixed systems was studied.Ultra-thin CONs not only improve the separation performance and transmission flux of polymer membranes,but also the nanometer thickness makes them have good compatibility with polymers.MMMs based on CONs still exhibit excellent separation performance in industrial gas mixture tests and long-term stability tests.