Fabrication Of 2D Metal-Organic Framework Ni₃(HITP)₂ Membranes For Gas Separation

The increase in global energy and environmental issues has led to the need for many important gas separation processes,such as the recovery of H₂ from petrochemical and the capture of CO₂.For these processes,membrane separation technology is considered to be one of the most promising methods from both practical and scientific point of view,which is a great need for energy-saving,efficient and environmentally friendly separation processes.However,the development of membranes with effective separation performance remains a huge challenge.A variety of membrane materials have been developed,such as polymers membranes,zeolite membranes,carbon membranes,silica membranes,metal organic framework(MOF)membranes,graphene oxide(GO)membranes and mixed matrix membranes(MMMs),etc.,which are used in gas and liquid separation both showed excellent separation performance.In recent years,ultra-thin membranes have attracted the attention of researchers because of their ability to overcome the upper bound of permeability/selectivity.Therefore,various materials have been explored to fabricate such ultra-thin separation membranes,including GO,covalent-organic frameworks(COFs),Mo S₂ and metal-organic frameworks,etc.The separation membrane prepared by the traditional method cannot achieve large area synthesis and as thin as possible.As a new member of the two-dimensional(2D)materials,2D MOF nanosheets have received more and more attention due to their large internal surface area,uniform pores,nano-sized cavities,thermal stability and chemical customization.In particular,2D MOF nanosheets possess many active sites on the surface,which are very important for gas storage,sensors,chemical catalysis,adsorption and small molecule separation.In this paper,we mainly prepared three kinds of separation membranes from 2D layered Ni₃(HITP)₂.Among the large number of MOFs,there are a little layered,easy to exfoliation and chemically stable2D MOFs.Based on the above mentioned reasons,we finally chose 2D Ni₃(HITP)₂reported by Dinca etal.The researches on Ni₃(HITP)₂ are concentrated in its electrical conductivity and application of lithium-sulfur battery separators and sensor devices fields.In this article,we conducted research on membranes of Ni₃(HITP)₂ for gas separation.We obtained membranes of the MOF with better separation performance on a rigid substrate through the top-down method and interfacial growth method of the MOF.The content of this thesis are described in detail as following:(1)We developed the filtration method to fabricate a uniform Ni₃(HITP)₂membrane on ordered macroporous AAO successfully.To fabricate the membrane,we obtained the Ni₃(HITP)₂ nanosheets via a soft-physical method.The Ni₃(HITP)₂membrane shows high permeance and selectivity of CO₂ over N₂,as well as good selectivity of H₂ over N₂.The ideal separation selectivty of CO₂/N₂ and H₂/N₂ from single gas permeance are 13.6 and 7.8 respectively.The membrane also showed good stability,durability and reproducibility,which are of potential interest for practical applications in the CO₂ separations.(2)2D Ni₃(HITP)₂ nanosheets based membranes for gas separation was lack of strong interlayer interaction between adjacent nanosheets,which will lead to poor mechanical stability of the membranes.The preparation of 2D separation membranes with excellent mechanical stability and defect-free layer stacking is still a huge challenge.Considering the surface of graphene oxide(GO)has various oxygen-containing functional groups,such as hydroxyl,carboxyl and epoxy groups,as well as its inherent structural flexibility,chemical and mechanical stability,and unique surface characteristics.We used a GO-assisted strategy to repair MOF nanosheets-based membrane for gas separation.The Ni₃(HITP)₂-GO membranes are highly continuous and compact.The membrane shows high permeance and selectivity of CO₂ over N₂,as well as good selectivity of H₂ over N₂.The stability of the membrane was significantly improved by introducing GO.(3)In this section,we report a simple,effective,and environmental-friendly method for the fabrication of high-quality 2D MOF via contra-diffusion method.The as-prepared membrane is highly continuous and compact.The membrane exhibited CO₂ permeance of 1.59×10^-6 mol m^-2 s^-1 Pa^-1 and excellent selective permeability of CO₂ over N₂ and CH₄.The ideal separation selectivtys of CO₂/N₂ and CO₂/CH₄ are10.2 and 6.9 respectively in single gas.In addition,the membrane exhibited gas separation performance with long-term stability and robustness.The new approach holds much promise for further development of the fabrication of high-quality metal-organic frameworks membranes for practical gas separation applications.