Humidity-induced significant microstructural reordering in partially reduced graphene oxide: Insights on water permeation mechanism

Abstract

Interaction of water and water-based solvents with graphene oxide (GO) has attracted much attention, due to the ability of GO to serve as a highly effective water filtration membrane. In this work, we study the evolution of the structure of GO in a partially reduced form, before and after being hydrated in high humidity conditions. X-ray diffraction (XRD) studies reveal that progressive thermal reduction leads to the increase in the microstructural disorder in the stacking of GO flakes. However, upon hydration of partially reduced GO, microstructural ordering is revealed. This ordered state is characterized by two XRD peaks with substantially smaller full-width-at-half-maximum (FWHM), when compared to the pre-hydration state. The peak corresponding to the sp3 regions has larger d-spacing of ∼9.7 Å and an FWHM ∼6 times smaller compared to pre-hydration state, while the other peak corresponds to the ordered sp2 regions with a d-spacing of ∼3.3 Å, observed at the characteristic graphitic peak position. Gravimetry studies on suspended films reveal both accelerated and diminished water permeation rates upon annealing when compared to unreduced GO films, which can be attributed to void-assisted permeation in the microstructurally disordered films. The hydrated films in a similar way show a permeation behavior that involves either the increase or decrease in water permeation rates in comparison with pre-hydrated samples. We reconcile to the gravimetry outcomes by suggesting the possibilities of both super-permeating channels and void assisted permeation, and the contribution of each of the mechanisms to the permeation flux.

Intercalated water mediated electromechanical response of graphene oxide films on flexible substrates

“…Further, for rGO-180 sample, an additional peak tending toward the graphitic peak appears at ∼18.10 • , which is characterized by a much smaller d-spacing (4.89 Å). This observation of dual peaks with two-interlayer separations in rGO is consistent with literature reports and corresponds to the simultaneous existence of spatially-segregated oxygencontaining regions as well as macroscopic regions which are devoid of defects [32,35,36]. Figure 1(c) shows the FTIR spectrum of transmittance (%) versus wavenumber for GO and rGO films on PDMS substrate.…”

“…The intensity of this distinct peak in GO reduces and the peak becomes broader with FWHM of the peaks increasing from 0.64 • (GO) to 3 • and 2.35 • (for rGO-150 and rGO-180, respectively). This broadening can be attributed to a partial breakdown of the long-range order of the GO film, as the film gets divided into vertical assembly of crystallites with fewer layers per crystallite [35]. Further, for rGO-180 sample, an additional peak tending toward the graphitic peak appears at ∼18.10 • , which is characterized by a much smaller d-spacing (4.89 Å).…”

Dielectric response and proton transport in water confined in graphene oxide

“…In thermally annealed GO films, both voids and interlayer spaces play a role in water vapor permeation. 24 Further, the dominance of interlayer channels over voids was shown for ion transport through partially reduced GO films immersed in water. 25 Furthermore, theoretical treatments of water intercalation in GO always assume an idealized configuration with water present between successive layers of GO.…”

Percolative proton transport in hexagonal boron nitride membranes with edge-functionalization

“…† The increase in FWHM is consistent with a lower number of h-BN layers in each crystallite. 40 In GO membranes, which are well-studied in literature, water intercalation progressively increases the spacing to 1 nm. 4,9 To explore whether water intercalates h-BN membranes, we performed X-ray diffraction studies on these membranes prepared in different humidity environments.…”