(709e) High-Performance Thin Film Composite (TFC) Membranes: Design Consideration Underneath the Polyamide Thin Film

Despite the commercial success of thin-film composite (TFC) technique for reverse osmosis (RO) and nanofiltration (NF) membrane production, overcoming the longstanding “trade-off” relationship between permeability and selectivity of TFC membranes remains a global challenge. Extensive research efforts have been put on altering the layer formation chemistry or intrinsic nanostructure to simultaneously improve its permeability and selectivity, but the critical role of the underlying porous substrate on the membrane separation performance was often overlooked. Not only formation of the polyamide layer is greatly affected by the substrate surface properties and pore structures, water transport through the TFC membrane is also largely governed by the structural feature of the substrate underneath the polyamide layer.

In this study, we firstly investigated how the configurations of the porous substrate influenced the desalination performance of the TFC membrane. Comparing to flat sheet membrane substrates, hollow fiber substrates were found to possess positive impact in terms of both water permeability and salt rejection, provided that the fiber mechanical strength is sufficient to withstand high pressure operation. Subsequently, we demonstrated the relationship between the substrate surface pore profile and the TFC membrane separation behavior. Manipulating the substrate surface pore profile i.e. surface porosity, pore number density, etc. for water flow path improvement was proved efficient in enhancing the TFC membrane water permeability. Afterwards, we extended the idea of flow path improvement from optimizing conventional polymeric substrates to the structural design of nanomaterial-based membranes. Nanotube/nanowire- or nanosheet-based interlayers were introduced to substitute the conventional polymeric membrane substrate underneath the polyamide thin film, with its influence on the TFC membrane performance systematically investigated. By optimizing the structure of the underlying nanomaterial-based interlayer and the flow path underneath the polyamide layer, TFC membranes with outstanding water permeability as high as 80 L m^-2 h^-1 bar^-1 and monovalent/ divalent ion selectivity above 20 was obtained. This study clarifies ambiguities concerning the effects of the underlying porous substrate as well as the nanomaterial involvement on the TFC membrane performance, and provides insight into designing highly permeable and selective TFC membranes.