The structure of graphene oxide membranes in liquid water, ethanol and water–ethanol mixtures

Zhang

et al. 2018

Trans. Tianjin Univ.

Graphene oxide (GO) contains numerous functional groups that facilitate the intercalation of polar solvents. The properties and applications of GO are closely related to its interlayer spacing. We report on the changes in the interlayer spacing of GO after the adsorption of water molecules and the polar organic solvents C 2 H 6 O 2 (EG), C 3 H 7 NO (DMF), C 5 H 9 NO (NMP). Experiments were conducted to investigate the variations in the functional groups and structure of GO after solvent adsorption, and they play a vital role in modeling and verifying the results of molecular dynamics simulation. The most stable GO structures are obtained through molecular dynamics simulation. The expansion of the interlayer spacing of GO after the adsorption of monolayer solvent molecules corresponds to the minimum three-dimensional size of the solvent molecules. The spatial arrangement of solvent molecules also contributes to the changes in interlayer spacing. Most adsorbed molecules are oriented parallel to the carbon plane of GO. However, as additional molecules are adsorbed into the interlaminations of GO, the adsorbed molecules are oriented perpendicular to the carbon plane of GO, and a large space forms between two GO interlayers. In addition, the role of large molecules in increasing interlayer spacing becomes more crucial than that of water molecules in the adsorption of binary solvent systems by GO.

Section: Relationship Between the Interlayer Spacing Of Go And The Sisupporting

confidence: 73%

Effects of Solvent Molecules on the Interlayer Spacing of Graphene Oxide

Zhang

et al. 2018

Trans. Tianjin Univ.

“…51 Film thicknesses were calculated from solution volume and GO concentration using d -spacings for hydrated GO measured by X-ray diffraction (XRD), which were consistent with literature reports (see Section S1 of the SI). 52–54 Selected film thicknesses were confirmed directly by atomic force microscopy (AFM) (Figure 1f), confirming accurate control over GO film thickness. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) analyses of the GO starting material are provided in Figure 1b–d, and show the characteristic spectra for GO with a C:O atomic ratio of ~2.1.…”

Section: Resultsmentioning

confidence: 57%

Breathable Vapor Toxicant Barriers Based on Multilayer Graphene Oxide

et al. 2017

There is tremendous interest in graphene-based membranes as protective molecular barriers or molecular sieves for separation technologies. Graphene oxide (GO) films in the dry state are known to be effective barriers for molecular transport and to expand in the presence of moisture to create enlarged intersheet gallery spaces that allow rapid water permeation. Here we explore an application for GO membranes as water-breathable barrier layers for personal protective equipment, which are designed to allow outward perspiration while protecting the wearer from chemical toxicants or biochemical agents in the local environment. A device was developed to measure permeation rates of small-molecular toxicants in the presence of counter-current water flow simulating active perspiration. The technique was applied to trichloroethylene (TCE) and benzene, which are important environmental toxicants, and ethanol as a limiting case to model very small, highly water-soluble organic molecules. Submicron GO membranes are shown to be effective TCE barriers, both in the presence and absence of simulated perspiration flux, and to outperform current barrier technologies. A molecular transport model is developed, which suggests the limited toxicant back-permeation observed occurs not by diffusion against the convective perspiration flow in hydrophobic channels, but rather through oxidized domains where hydrogen-bonding produces a near-stagnant water phase. Benzene and ethanol permeation fluxes are higher than those for TCE, likely reflecting the effects of higher water solubility and smaller minimum molecular dimension. Overall, GO films have high water breathability relative to competing technologies and are known to exclude most classes of target toxicants, including particles, bacteria, viruses, and macromolecules. The present results show good barrier performance for some very small-molecule species, but not others, with permeation being favored by high water solubility and small minimum molecular dimension.

“…The structure of GO membranes in liquid solvents is found to be quite dependent on the liquid molecules. While GO membranes are easily hydrated by water, intercalation of alcohols is hindered and the insertion of ethanol into the membrane is limited to only one monolayer [ 21 ]. For GO membranes in contact with solution or humid air, the interlayer gallery changes upon hydration.…”

Section: Atomic Structures Of Graphene Oxidementioning

confidence: 99%

Graphene Oxides in Filtration and Separation Applications

2015

Graphene Oxide

Graphene oxides feature much richer structural and physiochemical properties than the two-dimensional crystal graphene they are derived from. The stacked structures as well as functional groups and defects in the monatomic layers lead to a porous microstructure and engineerable channels for selective transport of water, ions, and gases across the graphene oxide membranes. Additional merits include their facile fabrication, low cost, and fl exibility. Recent efforts in exploring the structure-property relationship of these materials and environment and energyrelated applications not only demonstrate excellent balance between the permeability and selectivity of fl uid transport through the graphene oxide membranes, but also deepen our understanding of the molecular transport mechanisms down to the nanoscale. In this chapter we review some of the major theoretical and experimental advances in this fi eld, along with our perspectives for the future development.