Biomimetic Functionalized Membrane Enabling Selective Water Transport by Molecular Recognition

Abstract

Since clean and fresh water is essential for all-humans, the technology that treating contaminated water has been actively investigated. Among several candidates, membrane-based water treatment considered as an important technology because it is considered as a green technology. Numerous studies have been conducted to develop the membrane that achieve both high permeance and selectivity. Especially, biomimetic membrane that emulate the feature of biological proteins has emerged on membrane technology with a hope for the ultrafast water transport with high selectivity. Biological protein called aquaporin (AQP) that exhibiting high water permeability with total ionic rejection have been embedded in artificial membranes for fabricating biomimetic desalination membranes. However, there are challenges to overcome with the goal to transfer their activity at non-biological conditions, or to fabricate mechanically strong biomimetic membrane. Parallel to these investigations, recent research on biomimetic desalination membranes is mainly focused on finding appropriate sold-state scaffold for the membrane and choosing the incorporation method between the protein and the scaffold. In each chapter, I proposed novel approaches for fabricating biomimetic desalination membrane. I believe that the approach presented here can be used to guide the development of a new biomimetic materials and will bring fresh insight to further the development of desalination membrane. The contents of each chapter are summarized as shown below.

In Chapter 2, I examined the feasibility of graphene oxide (GO) membrane as a solid-state scaffold for biomimetic membrane. GO was incorporated with the functional peptides with cobalt-ion recognition capability. The layered structure of GO provides molecular pathways and carboxylation of GO contributed for more effective peptide incorporation. With this study, I confirmed that GO can be appropriate solid-state scaffold for the biomimetic desalination membrane.

Chapter 3 deals with the design and fabrication of GO-based membrane with a surface-tethered peptide motif designed to mimic the water selective filter of natural aquaporins. The short RF8 (RFRFRFRF, where R and F represent arginine and phenylalanine, respectively) octapeptide is a concentrated form of the core component of the aromatic/arginine water selective filter in aquaporin. The resulting GO-RF8 showed superior permeation flux and high selectivity over dye molecules similar to natural aquaporin (AQP). Molecular dynamics simulation revealed the unique configuration of RF8 peptides and the transport of water in GO-RF8 membranes, supporting that RF8 effectively emulates the core function of aquaporins.

Chapter 4 introduces an AQP-based biomimetic high-pressure desalination membrane by tethering AQP-carrying red blood cell membrane (RBCM) vesicles onto GO. RBCMs with AQPs are incorporated into GO based on the molecular recognition between the integrin of RBCM and Arginine-Glycine-Aspartate (RGD) ligand on the GO surface. RBCMs are inserted between GO layers through the material-specific interaction between integrin of RBCM and RGD ligand, thus ensuring sufficient coverage of channels/defects in the GO for the full functioning of the AQPs. The integrity of the GO-RBCMs binding can provide mechanical strength for enduring high-pressure reverse-osmosis conditions for treating large amounts of water. This biomimetic membrane exhibits 99.1% NaCl rejection and a water permeance of 7.83 L m-2 h-1 bar-1 at 8 bar with a 1000 ppm NaCl feed solution, which surpasses the upper-bound line of current state-of-the-art membranes.