In degassed water graphene re-aggregation is drastically slowed down due to the small intergraphene attractive dispersive forces (a consequence of graphene two-dimensional character) and the stabilizing electrostatic repulsion. As has been reported before for many hydrophobic objects, (i.e. hydrocarbon droplets 11 , 12 or air bubbles 13 ) graphene becomes electrically charged in water as a consequence of the spontaneous adsorption on its surface of OH -ions coming from graphenide oxidation and water dissociation. As two graphene flakes come together, they experience a repulsive force due to the overlap of their associated counterion clouds.Accordingly, graphene can be efficiently dispersed in water at a concentration of 0.16 g/L with a shelf life of a few months.The pH values after graphene transfer to water is very revealing. While the system resulting from the mixture with non-degassed water (left vial of Fig. 1b) has a pH close to 11, stable graphene suspensions have a pH close to neutrality (pH between 7 and 8; right vial of Fig. 1b). As the same amount of OH -is produced in both cases after graphenide oxidation, the remarkable difference in pH is attributed to the adsorption of OH -on the suspended graphene flakes. This hypothesis is supported by the electrophoretic mobility and zeta potential ζ of the graphene flakes. Negative ζ values (ζ = -45 ± 5) were observed at neutral pH conditions; on the contrary, charge reversal was observed in acidic pH environment (ζ = +4 ± 2 at pH 4). It could be argued that this ζ variation is due to the reduction of pH below the pK a of functional groups dissociated at basic pH. To discard this hypothesis, we measured ζ of water-dispersed graphene in presence of tetraphenylarsonium chloride, Ph 4 AsCl which contains a hydrophobic cation known to readily 3 adsorbs on hydrophobic surfaces 14 . As reported in Table 1, we observed a progressive increase in ζ with increasing concentration of the hydrophobic cation, with charge reversal at sufficiently large cation concentrations. Stability of SLG iw is determined by the interaction between the individual graphene plates. In regular laboratory conditions, gases dissolved in water (about 1 mM) adsorb on the graphene surface, inducing long-range attractive interaction between the dispersed objects and promoting aggregation (a, bottom left, gas bubbles and ions are not at scale). On the contrary, if water is degassed (removing dissolved gases) water-ions readily adsorb on the graphene surface, conferring a certain charge to the dispersed objects. The repulsive electrostatic interaction favors the stability of the dispersed material (b) Left vial: mixture of graphene in THF after addition to water which was not degassed. The aqueous dispersion is not stable and black aggregates visible to the eye begin to form a few minutes after mixing. Right vial: stable dispersion of graphene in degassed water after THF evaporation. No evidence of aggregation is observed after several months of storage at room temperature (c) UV-visible absorption...

Biodegradability of graphene is one of the fundamental parameters determining the fate of this material in vivo. Two types of aqueous dispersible graphene, corresponding to single-layer (SLG) and few-layer graphene (FLG), devoid of either chemical functionalization or stabilizing surfactants, were subjected to biodegradation by human myeloperoxidase (hMPO) mediated catalysis. Graphene biodegradation was also studied in the presence of activated, degranulating human neutrophils. The degradation of both FLG and SLG sheets was confirmed by Raman spectroscopy and electron microscopy analyses, leading to the conclusion that highly dispersed pristine graphene is not biopersistent.

Chemical doping of graphene with small boron nitride (BN) domains has been shown to be an effective way of permanently modulating the electronic properties in graphene. Herein we show a facile method of growing large area graphene doped with small BN domains on copper foils using a single step CVD route with methane, boric acid powder and nitrogen gas as the carbon, boron and nitrogen sources respectively. This facile and safe process avoids the use of boranes and ammonia. Optical microscopy confirmed that continuous films were grown and Raman spectroscopy confirmed changes in the electronic structure of the grown BN doped graphene. Using XPS studies we find that both B and N can be substituted into the graphene structure in the form of small BN domains to give a B-N-C system. A novel structure for the BN doped graphene is proposed.