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Download or read book Macroscopic Graphene Membranes with Tunable Nanopores for Highly Selective Mass Separation written by Doojoon Jang and published by . This book was released on 2018 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Membrane-based filtration enables energy-efficient separations of solutes, solvents, or gases, benefiting a wide range of applications including water desalination, nanofiltration, hemodialysis, solvent-based separation, or natural gas purification. Semipermeable polymeric desalination membranes rely on solution-diffusion mechanism to separate water from salts, where selective transport of species arises from their solubility and diffusivity in polymer phase. Despite the remarkable progress in materials, structure, and separation process over the past few decades, today's membranes are subjected to intrinsic challenges ranging from resolving the trade-off between permeability and selectivity to maintaining robust operation with high stability and low fouling. Two dimensional materials have the potential to address some of the above challenges by offering a fundamentally new mechanism to control nanofluidic transport with sustainable nanoscale pores, thereby presenting a platform for next-generation reverse osmosis (RO) or nanofiltration (NF) membranes. Although theoretical investigations of great breadth and depth have been pursued to understand mass transport across the atomically thin materials, experimental efforts are required to engineer and tune nanopore structure in macroscopically large graphene membranes and understand the resulting transport characteristics. Moreover, the effects of interplay between graphene nanopore structure and porous support layer on membrane transport properties need to be considered to identify the structure-function relationship of the nanoporous graphene membranes. This thesis aims at controlling selective graphene nanopore structure for high permeability and selectivity and understanding the tunable membrane transport properties. A two-step process of ion bombardment and oxygen plasma is carried out to introduce a high density of nanopores in large-area graphene membranes. Pore creation parameters are thoroughly explored to investigate the influence on pore size and density. The resulting transport properties of graphene membranes can be tuned to achieve high permeance to water, comparable to that of NF membranes, and highly selective transport of monovalent ions over organic molecules. Nanopore structure introduced in graphene membranes is inspected to quantitatively relate the pore creation parameters with the resulting pore size distributions. A multiscale transport model is constructed to investigate the interplay between nanoporous graphene and support pores that governs osmotic water flux and diffusive solute transport. Internal concentration polarization of draw solutes estimated by the model suggests that achieving narrowly distributed graphene pores with minimal leakage is essential to optimal operation of high-flux asymmetric graphene membranes under forward osmosis. Sterically governed molecular assembly is explored to mitigate residual solute leakage across large, non-selective pores for enhanced membrane selectivity. High molecular weight polymers can electrostatically or covalently assemble across nanoscale defects of graphene to narrow down the effective pore size distribution, sterically and electrostatically hindering transport. Multi-step size-selective polyelectrolyte assembly enables >/=99% retention of divalent ions and organic molecules, promising the potential of graphene in desalination, nanofiltration or organic solvent nanofiltration (OSN). With experimental/theoretical means to characterize membrane structure and transport properties, this thesis forms the basis for regulating nanofluidic mass transport with tunable nanopores and developing atomically thin separation membranes with high selectivity and permeability.