Confined Structures and Selective Mass Transport of Organic Liquids in Graphene Nanochannels

Abstract

Selective transport of liquids is an important process in the energy and environment industry. The increased energy consumption and the demands of clean water and fossil fuels have urged the development of highperformance membrane technologies. Nanoscale channels with the critical size for molecular sieving and atomistically smooth walls for significant boundary slippage are highly promising to balance the tradeoff between permeability and selectivity. In this work, we explore the molecular structures and dynamics of organic solvents and water, which are confined within nanoscale two-dimensional galleries between graphene or graphene oxide sheets. Molecular dynamics simulation results show that the layered order and significant interfacial slippage are universal for all molecular liquids, leading to notable flow enhancement for channels with a width of few nanometers, in the order of ethylene glycol > butanol > ethanol > hexane > toluene > water > acetone. The extracted dependence of permeability, selectivity on the channel width, and properties of molecular liquids clarify the underlying mechanisms of selective mass transport in nanofluidics, which help to understand and control the filtration and separation processes of molecular liquids. The performance of graphene oxide membranes for permeation and filtration is finally discussed based on the calculated flow resistance for pressure-driven flow or molecular diffusivity for diffusive flow, as well as the solubility and wettability of membranes.

Swelling properties of graphite oxides and graphene oxide multilayered materials

“…16B. 239 6.5 Å, 284 8.7 Å, 280 10.0 Å, 281 11.0 Å, 282 13.5-14.0 Å 279,281 Protonic polar solvents. Alcohols Methanol 9.1 Å, 264 All three structures shown in Fig.…”

Snap-through in Graphene Nanochannels: With Application to Fluidic Control

“…From this perspective, such large flow velocities and pressure gradients are standard for nonequilibrium MD simulation. ,, Another possible reason is that the simulation system is entirely ideal, in which the surfaces of graphene layers are completely smooth at the atomic scale and the slip effect is much larger than that in the real experimental system. The synthesized graphene layers in experiments usually contain some additional functional groups and defects, as well as impurities, on their surface, which may weaken the slip effect and therefore significantly reduce the flow velocity under the same pressure gradient. , …”

“…The filtration effects of parallel stacked nanochannels, nanoslits, and nanopores have been widely explored. However, in most of the previous studies, nanochannels in graphene laminates are modeled as nondeformable walls regardless of their flexibility and fluid–solid coupling effect in the flux. ,,,, Due to the extremely low out-of-plane stiffness of graphene sheets, uneven structures, such as ripples, wrinkles, and crumples, are plentiful in the stacked graphene membrane. , Besides, the wrinkled wall can be deformed under pressure during the liquid flow process, and in turn, the deformation of the wall affects the liquid flow process, as well as the function of the membrane (i.e., molecule selection). Therefore, the influences of membrane flexibility and wrinkled structures on liquid transport and filtration efficiency, as well as the regulating effect of fluid flow on flexible wrinkled structures, need further investigation.…”

“…However, in most of the previous studies, nanochannels in graphene laminates are modeled as nondeformable walls regardless of their flexibility and fluid−solid coupling effect in the flux. 3,12,18,27,28 Due to the extremely low out-of-plane stiffness of graphene sheets, uneven structures, such as ripples, wrinkles, and crumples, are plentiful in the stacked graphene membrane. 19,29 Besides, the wrinkled wall can be deformed under pressure during the liquid flow process, and in turn, the deformation of the wall affects the liquid flow process, as well as the function of the membrane (i.e., molecule selection).…”

Thin-Film Composite Membrane Prepared by Interfacial Polymerization on the Integrated ZIF-L Nanosheets Interface for Pervaporation Dehydration

“…The combustion of fossil fuels plays a substantial role in this. − The energy needs of the industry, combined with the awareness of the devastating effect of using nonsustainable energy sources, spurred an enormous demand for green fuels. Bioethanol produced from the fermentation of biomass is an alternative candidate for fossil fuels. − Unfortunately, apart from ethanol, a large quantity of water is produced in the fermentation reaction. To obtain ethanol with high heat value, dehydration is unavoidable.…”