Insights into the Stability of Graphene Oxide Aqueous Dispersions

Abstract

Understanding graphene oxide's stability (or lack thereof) in liquid solvents is critical for fine-tuning the material's characteristics and its potential involvement in future applications. In this work, through the use of structural and surface investigations, the alteration of the structural and edge-surface properties of 2D graphene oxide nanosheets was monitored over a period of eight weeks by involving DLS, zeta potential, XRD, XPS, Raman and FT-IR spectroscopy techniques. The samples were synthesized as an aqueous suspension by an original modified Marcano-Tour method centred on the sono-chemical exfoliation of graphite. Based on the acquired experimental results and the available literature, a phenomenological explanation of the two underlying mechanisms responsible for the meta-stability of graphene oxide aqueous dispersions is proposed. It is based on the cleavage of the carbon bonds in the first 3-4 weeks, while the bonding of oxygen functional groups on the carbon lattice occurs, and the transformation of epoxide and hydroxyl groups into adsorbed water molecules in a process driven by the availability of hydrogen in graphene oxide nanosheets.

Keywords: aqueous dispersions; graphene oxide; sono-chemical exfoliation; stability; structural characterisation.

Figure 1

Schematic representation of the synthesis process of the obtained superior (GO_SUP) and inferior (GO_INF) GO aqueous suspensions.

Figure 2

SEM image of the edge of a self-assembled GO film showing the wrinkled nanosheets at the edge of the microstructure.

Figure 3

Size distributions by intensity obtained for GO suspension fractions GO_SUP and GO_INF immediately after the synthesis process was done (left) and 8 weeks later (right).

Figure 4

ζ−potential variation for GO suspension fractions GO_SUP (right) and GO_INF (left) over the course of 8 weeks after the synthesis process.

Figure 5

The time evolution of the D and G band intensity ratio from the Raman spectra of dried GO_SUP (left) and GO_INF (right) samples.

Figure 6

The FWHM values obtained after processing the D (a,b) and G bands (c,d) from the Raman spectra of dried GO_SUP and GO_INF samples.

Figure 7

FT−IR spectra recorded weekly over the considered time period for the dried GO_SUP (left) and GO_INF (right) samples.

Figure 8

The intensity ratio of the functional group absorption bands and the 1640 cm⁻¹ reference band for the dried GO_SUP (left) and GO_INF (right) samples over a time period of eight weeks after synthesis.

Figure 9

Calculated interlayer distance variation of the GO sheets over the course of eight weeks after the synthesis.

Figure 10

Deconvoluted C1s core-level XPS spectra of the dried GO_SUP (left) and GO_INF (right) samples obtained immediately after synthesis.

Figure 11

Peak ratios of the deconvoluted C1s core-level spectra of the dried GO_SUP (left) and GO_INF (right) samples over the course of the four weeks after the synthesis.

Figure 12

Deconvoluted O1s core-level XPS spectra of the dried GO_SUP (left) and GO_INF (right) samples obtained immediately after synthesis.

Figure 13

Evolution of the ratios of each bond type identified in the deconvoluted O1s core-level spectra of the dried GO_SUP (left) and GO_INF (right) samples over the course of the four weeks after the synthesis.