On the Gelation of Graphene Oxide

Abstract

In the past half decade, graphene oxide (GO), a precursor of graphene, 1À4 has attracted a great deal of attention due to its unique structure and outstanding physical and chemical properties. 5À8 Particularly, GO behaves like an amphiphilic macromolecule with hydrophilic edges and a more hydrophobic basal plane, 9À11 which makes it an attractive building block for the construction of various supramolecular architectures. 12,13 Furthermore, the two-dimensional (2D) structure of GO sheets provides them with various new supramolecular behaviors compared with conventional low-dimensional counterparts. Although GO sheets have been assembled into various macrostructures, such as LangmuirÀBlodgett (LB) films and paper-like films, 14À17 their 3D assembly behavior has not yet been clearly revealed. 18 We have first reported the 3D assembly of GO sheets in water solution by adding poly(vinyl alcohol) (PVA) as a crosslinker, forming a pH-sensitive supramolecular hydrogel. 19 Hydrogen bonding between GO sheets and PVA chains is believed to be responsible for the formation of the hydrogel. Recently, single-stranded DNA was also found to be a good cross-linker for preparing a GO/DNA composite hydrogel, in which πÀπ interaction was the dominant driving force. 20 Similarly, hydrogels based on chemically concerted graphene (CCG) have also been reported by us and other groups. 21À25 These examples reflect that GO and CCG are good gelators. However, the gelation of GO sheets has not yet been studied extensively and the fundamental roles behind gelation phenomena have also not been clearly revealed. Here, we report a systematical study on GO gelation. The GO-based hydrogels were prepared by acidification or adding small organic molecules, polymers, or ions as crosslinkers. The effects of different driving forces (e.g., hydrogen bonding, electrostatic interaction, and coordination) and lateral dimensions of GO sheets on GO gelation are discussed.

Biomimetic superelastic graphene-based cellular monoliths

“…Water-soluble GO appears to be the ideal precursor for freeze casting. However, we found that directly freezing of GO dispersions only resulted in a randomly oriented porous structure, which is consistent with a previous report 34 . The monoliths directly resulted from unreduced GO displayed poor mechanical strength and small recoverable deformation region (Supplementary Methods).…”

Flexible free-standing graphene paper with interconnected porous structure for energy storage

“…The arrangement of graphene sheets in solution/gel is attributed to the balance between electrostatic repulsion (originating from the functional group on the edge of graphene sheets) and interaction forces arising from hydrogen bonding and π-π interaction. 32,33 When the binding interaction is reinforced by filtration and becomes the main driving force, the graphene sheets in the gel tend to arrange a layered structure. Once the water was removed by air drying, the intersheet interaction could be further reinforced due to the partial flattening of the graphene sheets, forming a compact layered structure.…”

Three-Dimensional Graphene Interconnected Structure, Fabrication Methods and Applications: Review

“…Critical analysis of the results do revel that the carbon nanowall growth evolution comprised: nucleation, growth and interconnection of graphite nanosheets onto nanoislands and subsequently coagulation of as-grown graphite nanosheets. They reported the highest CNW growth rate within the first 1-3 min, whereas a steady thickness was observed below 10 nm throughout the growth [38]. Furthermore, the OH radicals were vital during the initial nucleation stage, however , oxidation of the CNWs was observed if the OH radicals were in excess.…”

“…Junhong Cheng and team [38] managed to highlight that with direct current plasma enhanced CVD and negative glow discharge, vertical graphene sheets can be grown on conductive substrates for instance Au and stainless steel. Vertical graphene patterns were designed by artificially designing the surface electric field distribution.…”

“…Furthermore, the OH radicals were vital during the initial nucleation stage, however , oxidation of the CNWs was observed if the OH radicals were in excess. Therefore, for high crystalline CNWs, optimum feed gas relative humidity of 40% and optimum current density of 9.17 A/m 2 was reported [38]. These graphene patterns were then used in a field-effect transistor device for detecting low concentration gases.…”