Abstract
Graphene oxide (GO) membranes have shown great potential in the applications of water filtration and desalination. The flow behavior and structural properties of water molecules through GO nanochannels are still under debate. In this work, molecular dynamics simulations were performed to explore the effects of interlayer spacing and oxidation degree of GO nanochannels on water transport. The results show that GO nanosheets have strong adsorption capacity. The adsorbed layer of water molecules on GO surface is thermodynamically stable and not easy to flow. When the interlayer spacing falls into the range of 0.6 ~ 1.0nm, water molecules form into single or double adsorbed layers between two GO nanosheets. When the interlayer spacing is bigger than 1.2nm, the other water layers in the middle of nanochannel become disordered. Taking the separation performance based on size exclusion into consideration, the most suitable interlayer spacing for water nanofiltration is approximate 1.2nm, which has one flowing layer of water molecules. Oxygen-containing groups are unfavorable for water permeation, as more and more hydrogen bonds prevent water flowing on GO surface with the increasing oxidation degree. Our simulation results may help to improve the design of GO nanofiltration membranes for water treatment.
Highlights
Graphene has unique optical, electronic and mechanical properties as well as planar structure, and can be used for nano-filtration, water treatment, supercapacitors and photocatalysis[1,2,3,4,5]
Oxygen-containing groups are unfavorable for water permeation, as more and more hydrogen bonds prevent water flowing on Graphene oxide (GO) surface with the increasing oxidation degree
To understand the adsorption stability of water for pristine graphene (PG), the mean sojourn time (MST) of water molecules confined to their initial points in z-direction was analyzed, which is defined as where is set at 0.01 nm
Summary
Electronic and mechanical properties as well as planar structure, and can be used for nano-filtration, water treatment, supercapacitors and photocatalysis[1,2,3,4,5]. Graphene layered membranes are formed by stacking single layers of graphene with nanoscale interlayer spacing[6, 7]. This special laminated structure allows the permeance of water molecules and reject other molecules. The performance of desalination has been extensively studied by experimental and theoretical calculations[8, 9]. Since graphene is difficult to be exfoliated and agglomerated, its performance can be adjusted by introducing functional groups for efficient desalination, among which graphene oxide (GO) has been widely studied
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