Ultrathin Membranes Based On Manipulating Multiple Interfacial Interactions: Fabrication And Performance Improvement For Water/Alcohol Separation

The enhancement of membrane-technology competitiveness is critically dependent on developing high-performance membranes, which can be achieved by tuning the interfacial interactions within membrane. Specifically speaking, the tuning of interfacial interactions play vital roles in optimizing membrane structures, intensifying mass transfer mechanisms, and then acquiring high-performance membranes. This study focuses on the important issue of fuel ethanol production in energy and environment fields. In order to fabricate ultrathin membranes with high performance for water/alcohol separation, the approaches to regulating the interactions within different types of interfaces, and the integrated strategies of optimizing the mass transfer mechanisms via tuning multiple interfacial interactions are proposed. A series of ultrathin composite membranes/hybrid membranes with proper chemical structures and topographies were designed and fabricated by facile and mild methods, and achieved high efficiency separation of water/alcohol. This study is expected to offer theoretic and technological guidance and support to large-scale fabrication of highperformance water/alcohol separation membranes. The details are summarized as follows:The tuning of multiple interfacial interactions between separation layer-support layer: based on biomimetic adhesion method, dopamine and poly(ethylene imine)(PEI) were co-deposited on support layer for modification. Ultrathin composite membranes were fabricated with the subsequent coating of sodium alginate(SA) as separation layer. The simultaneous improvements of solution and diffusion mechanisms are rendered by the increased hydrophilicity of interface region and the optimization of free volume properties(due to the emergence of abundant electrostatic and hydrogen bond sites). As a result, the composite membrane shows a permeation flux of 1196 g/m2 h, and a separation factor of 1807. The separation factor is 29.6 times higher than that of the composite membrane with unmodified support layer.The tuning of multiple interfacial interactions between separation layer-separation layer:(1) inspired by the biological phenomenon of protein precipitation by tea polyphenol, gelatin(protein) and tannic acid(polyphenol) were selected as building blocks. Ultrathin composite membranes were fabricated via layer-by-layer(Lb L) selfassembly driven by hydrophobic interactions and hydrogen bonds. The introduction of multiple interactions at the interface affords the optimization of the chemical structure on membrane surface and the free volume properties, leading to the integrated intensification of solution and diffusion mechanisms. The resulting multi-layered membrane exhibits a permeation flux of 1336 g/m2 h and a separation factor of 658. Higher separation performance can be obtained at higher water contents, reaching a permeation flux of 2696 g/m2 h and a water content in permeate of 99.43 wt% at water content in feed of 30 wt%.(2) gelatin and graphene oxide were selected as the building blocks because of the well-matched structures. Ultrathin composite membranes were fabricated via the Lb L self-assembly driven by multiple interactions(electrostatic interactions, hydrogen bonds and hydrophobic interactions). The tuning of interfacial interaction strength confers the optimization of topological structures, leading to the intensification of diffusion mechanism. The resulting multi-layered membranes exhibit simultaneous enhancement of permeation flux and separation factor compared with gelatin control membrane.The tuning of multiple interfacial interactions between polymer matrix-filler:(1) zwitterionic polymer modified graphene oxide was synthesized by free radical polymerization and incorporated into polymer to fabricate ultrathin hybrid membranes. The zwitterionic groups optimize the membrane hydrophilicity; the electrostatic interactions and hydrogen bonds at the interface optimize the free volume properties and crystallinity. As a result, the integrated optimization of solution mechanism and diffusion mechanism is achieved. The membrane exhibits the simultaneous enhancement of permeation flux and separation factor with a permeation flux of 2140 g/m2 h, and a separation factor of 1370.(2) ultrathin hybrid membranes were fabricated by adding modifier during the sol-gel process of Ti Cl4 and achieving synchronous modification based on metal-catechol chelation. The modifier increases the hydrophilicity of hybrid membranes by introducing hydrophilicity groups, and meanwhile optimizes the free volume properties and interfacial morphology by manipulating the number of covalent bonds and hydrogen bonds between polymer matrix and filler. As a result, the integrated optimization of solution mechanism and diffusion mechanism is achieved. The membrane exhibits a permeation flux of 1403 g/m2 h, and a separation factor of 730.