Isolation by dialysis and characterization of luminescent oxidized carbon nanoparticles from graphene oxide dispersions: a facile novel route towards a more controlled and homogeneous substrate with a wider applicability^*

Graphene Oxide (GO) is a two-dimensional (2D) nanomaterial largely exploited in many fields. Its preparation, usually performed from graphite in an oxidant environment, generally affords 2D layers with a broad size distribution, with overoxidation easily occurring. Here, we investigate the formation, along the Hummers synthesis of GO, of carbon nanoparticles (CNPs) isolated from GO and characterized through morphological and spectroscopic techniques. The purification methodology here applied is based on dialysis and results highly advantageous, since it does not involve chemical processes, which may lead to modifications in the composition of GO layers. Using a cross-matched characterization approach among different techniques, such as x-ray photoelectron spectroscopy, cyclic voltammetry and fluorescence spectroscopy, we demonstrate that the isolated CNP are constituted by layers that are highly oxidized at the edges and are stacked due to<i>π</i>-<i>π</i>interaction among their aromatic basal planes and H-bonded via their oxidized groups. These results, while representing a step forward in the comprehension of the structure of long-debated carbon debris in GO, strongly point to the introduction of dialysis as an indispensable step toward the preparation of more controlled and homogeneous GO layers and to its use for the valorization of low molecular weight GO species as luminescent CNPs.