Systematic evaluation of different types of graphene oxide in respect to variations in their in-plane modulus

Abstract

Graphene oxide samples prepared in various laboratories following a diversity of synthesis protocols based on Brodie's (BGO) and Hummers/Offeman's (HGO) methods were compared in respect of their inplane moduli. A simple wrinkling method allowed for a spatial resolution <1.5 mm by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600 GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200 GPa for HGO types. This would suggest that there are no two equal GO samples and GO should not be regarded a compound but rather a class of materials with very variable physical properties. While large differences between Brodie's and Hummers/Offeman's types might have been expected, even within the group of Hummers/Offeman's types pronounced differences are observed that, based on 13 C solid-state NMR, were related to over-functionalization versus over-oxidation.

Brodie's or Hummers’ Method: Oxidation Conditions Determine the Structure of Graphene Oxide

“…Harsh reaction conditions usually lead to materials with different physical properties and a distorted carbon lattice due to over‐oxidation . However, we demonstrated that by controlling the temperature of the reaction the carbon framework could be preserved .…”

Graphite oxide swelling in molten sugar alcohols and their aqueous solutions

“…[49] Smaller number of defects in Brodie GO relative to Hummers GO is also supported by superior mechanical properties measured on individual Brodie graphene oxide flakes and multilayered membranes. [33] However, one needs to note that the effect of different impurities (first of all sulphur in HGO) on swelling properties of graphite oxides is not yet completely clear.…”

“…It should be noted here structural models of GO were proposed over past 20 years were mostly proposed based on studies of materials produced by Hummers oxidation, e.g. [9,14] However, BGO and HGO are different materials in respect to some key properties which include e.g swelling [29][30], exfoliation [30][31][32] and mechanical properties [33]. The difference between solvation/hydration properties of BGO and HGO was subject of several recent studies but remains to be poorly understood.…”

Immobilization of a Pd(II) complex on hydrophilic graphite oxide and its catalytic investigation in the Heck coupling reaction

“…Recently, the dependence of the physicochemical properties of GO on the synthesis method has been highlighted and considerable sample‐to‐sample variations were also demonstrated . However, all sorts of graphene oxides are hydrophilic materials.…”