Fabrication And Application Of Novel Two-dimensional Cu-TCPP Membranes

Membrane separation technology has been considered as a new environment-friendly separation process due to its advantages of high energy efficiency,good separation performance,low investment cost,and continuous operation.However,the preparation of polymer membranes with high permeability and selectivity is still a great challenge because of the inherent trade-off effect between the permeability and selectivity of traditional polymer membranes.The appearance of two-dimensional（2D）materials with atomic thickness has greatly promoted the development of membrane separation technology.Exerting precise control over in-plane pore size and interlayer structure of 2D membrane has proven to be of vital importance to precious molecular sieving.Metallic-porphyrin 2D material is a kind of metal-organic framework with stable structure composed of largeπ-conjugates.It not only possesses structural and functional diversity of common porphyrin molecules,but also forms extended 2D layered structure between metallic-porphyrin molecules through ionic bonding.Owing to the stacking effect between layers,two-dimensional Cu-TCPP crystals process narrowed in-plane pore size,which is expected to achieve precise molecular sieving.In this study,in view of the new requirements and challenges proposed by the development of membrane separation technology,we successfully prepared the well-intergrown,highly c-oriented and ultrathin 2D Cu-TCPP membrane with integrated structure by simple in situ solvothermal method and studied its gas separation performance and long-term operation stability.Main research results are as follows:（1）The Zn O buffer layer prepared by sol-gel method was served as nucleation sites of Cu-TCPP crystals on porousα-Al₂O₃ substrate.Experimental results demonstrated that the use of Cu（acac）₂ used as copper source instead of Cu（NO₃）₂ retarded the excessive crystal nucleation in the bulk solution during solvothermal process.In addition,the use of TEA was proven quite effective for concurrent promotion of the in-plane growth and suppression of the undesired out-of-plane growth of 2D Cu-TCPP membrane.The above results confirmed the feasibility of preparing well-intergrown,highly c-oriented ultrathin 2D Cu-TCPP membrane on Zn O buffer layer by in-situ solvothermal method.（2）The Zn O buffer layer prepared by calcination of Zn Al-NO₃ LDH precursor membrane was served as nucleation sites of Cu-TCPP crystals on porousα-Al₂O₃ substrate.Cu-TCPP membranes with different morphologies by adjusting the concentration of NH₃·H₂O during the synthesis of Zn Al-NO₃ LDH precursor.Our results indicated that prepared c-oriented Cu-TCPP membrane was highly uniform,well-intergrown and only 80 nm-thick.（3）Both single and mixed gas permeation tests were performed on prepared 2D Cu-TCPP membrane,which exhibited superior gas selectivities towards H₂/N₂（40.2）and H₂/CH₄（56.0）gas pairs at 453 K and 1 bar.Moreover,prepared 2D Cu-TCPP membrane showed impressive long-term stability with separation factor unchanged for 30 h at 453 K and 1 bar.The separation performance our 2D Cu-TCPP MOF membrane was superior to most pristine polycrystalline MOF membranes reported in the literature.