서강대학교

초록/요약

Aquaporin is pore-forming protein and ubiquitous in living cells. Fast water transport and high selectivity are the main features of aquparins, resulting from its unique structure suggesting an hourglass-shaped nanopores. The proposed thesis aims to study the fundamental of water permeation dynamics through bio-mimetic nanopores, mimicking aquaporins protein water channel, using molecular dynamics simulation technique. This thesis is divided into three parts as following, The first part aims to investigate water transport properties through hourglass-shaped nanopores affected by length. The length is a major parameter that affects on water transport in carbon nanotubes (CNTs). CNT membranes utilized in experiments often are as long as several micrometers, whereas molecular dynamics (MD) simulations allow to perform the CNTs of the nanometers in length. Thus, the necessity of studying the effect of the length on water transport properties at the nanoscale is appreciable, which can help to predict transport mechanisms within experimental length scales. Our study shows that water flow decreases with length due to hydrodynamic resistance at the entrances, which has large contribution on water flow. Moreover, it is found that water flux decreases as the length increases, which is consistent with recent experiment. Although single-layer nanoporous graphene has proven to be effective as a reverse osmosis desalination membrane, multilayer nanoporous graphene (MNPG) is economically affordable to be synthesized. The second part of thesis aims to understand water transport mechanisms through nanopores with cylindrical and hourglass-shaped geometries constructed by multilayer nanoporous graphene (MNPG). Furthermore, the hydrophobicity and hydrophilicity effects on water permeation through hourglass-shaped nanopores have been addressed. Our study shows that hourglass-shaped pore structure compared to straight ones constructed by multilayer graphene suggests more efficient design for achieving higher flux. It is also observed that hydrophilicity effect could virtually double the flux inside hourglass-shaped pore, resulting from strong hydrogen bonds. To date, only graphene and graphene oxide membranes have been extensively investigated as filtration membranes, a few studies attempted to investigate the Boron Nitrite (BN) monolayer. The third part of thesis aims to study water transport properties through hourglass-shaped pore structure in nanoporous boron nitrite (BN) and graphene multilayers as a function of layer spacing (d). An increase in water flux is evidenced as the gap between the layers increases, reaching a maximum of 41 and 43 ns-1 at d=6 Å, respectively. Moreover, the BN multilayer exhibits less flux compared to graphene due to large friction force and energy barrier as the layer spacing increases. As the solid-state ultra-fine pores are hourglass shaped as opposed to having a straight structure, little effort has been made on water permeation/desalination or gas separation through aquaporin-mimicking ultra-fine pores. Moreover, to the best of the authors’ knowledge, the existing studies on the water transport through hourglass-shaped pore structures are limited to the symmetric geometries. In order to benefit from the advantage of combining the properties of nanoporous graphene and aquaporin water channels, the forth part of this thesis aims to study designing a highly effective permeable membrane for water transport through asymmetric hourglass-shaped pores in a multilayer structure using MD simulation. In particular, we have examined the effect of the pressure difference on water transport through symmetric and asymmetric hourglass-shaped pores in multilayer graphene with a constant interlayer separation of 6 Å. The study findings revealed that the water flux linearly increases with pressure difference inside pore systems, indicating higher flux inside α=1/3 because of the long lasting hydrogen bonds, which result from low viscosity. On the other hand, it was found that the pore α=1/3 can transfer water molecules at higher flux compared to the symmetric hourglass-shaped pore. This may be attributed to the low viscosity resulting from the length effect.