Effect of the oxidation degree on self-assembly, adsorption and barrier properties of nano-graphene

Oxidized nano-graphene (nGO, lateral size about 200 nm) was synthesized from graphene nanoplatelets to evaluate the effect of sheet size and oxidation degree on self-assembly behaviour, adsorption and barrier properties of graphene. nGO samples having O/C atomic ratios between 0.11 and 0.49 were obtained. nGO water dispersions showed good stability and were effective to adsorb organic dyes. Bulk and porous self-assembled nGO samples were prepared through water evaporation and freeze-drying, respectively. For both processes, only higher oxidation degrees yielded self-standing structures. Nitrogen adsorption measurements demonstrated that self-assembly by water evaporation of highly oxidized graphene resulted in a relevant reduction of the BET specific surface area (about 2 m2/g), while freeze-drying promoted the formation of interconnected structures with higher BET specific surface area (about 120 m2/g). Barrier properties towards oxygen of nGO were demonstrated on free-standing nGO films and on nGO coatings applied on a polyethylene substrate.