Diffusion of Water Confined between Graphene Oxide Layers: Implications for Membrane Filtration

Abstract

Among the carbon-based two-dimensional (2D) materials, graphene oxide (GO) has been attracting growing interest because of its ability to be utilized in the field of water remediation. Therefore, an atomistic understanding of the transport properties of water in layered GO is pivotal for the development of novel GO membranes. Surprisingly, the very issue of the 2D self-diffusion of water confined between two GO sheets appears to be controversial, and simulations showing either a slowdown or no effect have been reported. In any case, the formation of hydrogen bonds, i.e., among the confined water and between water and the GO functional groups, was identified to control diffusion. However, the results of molecular dynamics (MD) simulations heavily depend on the forces used. Density functional theory (DFT) and empirical force fields are opposite when it comes to accuracy and numerical costs. As a compromise in the present study, we performed MD simulations using a DFT-based tight-binding method to investigate the diffusion of water confined between GO sheets. Specifically, we considered six GO/water models, differing in the ordering of the epoxide and hydroxyl groups as well as in the thickness of the water layer. For these models having GO interlayer distances between 8 and 12 Å, we find a reduction of the diffusion coefficient by a factor between 2 and 3 compared with bulk water. One possible origin of this effect is the temporary trapping of water within hydrogen-bonded water bridges between the GO sheets. The proposed mechanism should be taken into account in the development of, for instance, GO membranes for water remediation or applications in the field of selective transport in separation membranes.

Nanoconfinement effects on water in narrow graphene-based slit pores as revealed by THz spectroscopy

“…Therefore, we assign the experimentally observed ST2 band to bound water at the oxygen atoms of graphene oxide (see for example ref. 36, 71 and 84), which constitutes about 40% of the membrane. It is worth noticing that bulk water, in addition to confined water, was reported earlier for systems similar to ours, such as bulk graphite oxide and fully oxidized graphene membranes.…”

Fabric Comprised of Cotton Impregnated with Graphene Oxide and Coated with Polystyrene for Personal Moisture and Thermal Management

“…Two noticeable peaks in the G/P-C (GO) spectra (Figure b) existed at 1345 and 1600 cm –1 , which correspond to the typical D and G bands, respectively, and demonstrate that there was a GO nanosheet coating on the G/P-C fabric. The G band corresponds to the in-phase vibrations of sp 2 -hybridized C–C bonds in the 2-D hexagonal frame, while the D band represents the level of structural disorder in the carbon network caused by graphitic edges. , Conversely, the pure cotton fabric had a very low G-peak intensity and a comparatively small D band.…”

“…The G band corresponds to the in-phase vibrations of sp 2 -hybridized C−C bonds in the 2-D hexagonal frame, while the D band represents the level of structural disorder in the carbon network caused by graphitic edges. 25,26 Conversely, the pure cotton fabric had a very low G-peak intensity and a comparatively small D band.…”

Synthesis of Graphene-Based Nanocomposites for Environmental Remediation Applications: A Review

“…Further, various types of polymers are tried as a core material, along with organic solvents and inorganic metal oxides, as shown in Table 7 , to remove the above-mentioned limitations. Polymers, such as polyvinylidine fluoride, polysulfone, polyethersulfone, polyacrylonitrile, polypropylene, and polytetrafluoroethylene, offer a great design with high flexibility and stability to the membrane [ 206 , 207 , 208 , 209 , 210 ]. Furthermore, to improve the porosity, antibacterial, and anti-fungal activity, other additives such as metal oxide/graphene oxide nanocomposites and organic solvents were incooperated in membrane synthesis by numerous research groups [ 209 , 210 , 211 , 212 ].…”

“…Nanoparticles may be either coated onto the membrane surface or dispersed in the polymer solution before membrane casting, as shown in Figure 16 . Dispersing the GO–metal oxide nanocomposites into the polymer generally forms these composite membranes that are a suitable tool to improve the performance, such as permeability and selectivity, of polymeric membranes, due to changes in the surface properties of membranes, influencing the separation performance, excellent rejection of pollutants, and better antifouling behavior, as shown in Figure 17 [ 208 , 209 , 210 , 211 , 212 , 213 , 214 , 215 , 216 ].…”