Continuous Production of Functionalized Graphene Inks by Soft Solution Processing.

The continuous production of high-quality, few-layer graphene nanosheets (GNSs) functionalized with nitrogen-containing groups was achieved via a two-stage reaction method. The initial stage produces few-layer GNSs by utilizing our recently developed glycine-bisulfate ionic complex-assisted electrochemical exfoliation of graphite. The second stage, developed here, uses a radical initiator and nitrogen precursor (azobisisobutyronitrile) under microwave conditions in an aqueous solution for the efficient nitrogen functionalization of the initially formed GNSs. These nitrile radical reactions have great advantages in green chemistry and soft processing. Raman spectra confirm the insertion of nitrogen functional groups into nitrogen-functionalized graphene (N-FG), whose disorder is higher than that of GNSs. X-ray photoelectron spectra confirm the insertion of edge/surface nitrogen functional groups. The insertion of nitrogen functional groups is further confirmed by the enhanced dispersibility of N-FG in dimethyl formamide, ethylene glycol, acetonitrile, and water. Indeed, after the synthesis of N-FG in solution, it is possible to disperse N-FG in these liquid dispersants just by a simple washing-centrifugation separation-dispersion sequence. Therefore, without any drying, milling, and redispersion into liquid again, we can produce N-FG ink with only solution processing. Thus, the present work demonstrates the 'continuous solution processing' of N-FG inks without complicated post-processing conditions. Furthermore, the formation mechanism of N-FG is presented.

Role of peroxide ions in formation of graphene nanosheets by electrochemical exfoliation of graphite.

This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO(-)) leads to the formation of highly nucleophilic peroxide ions (O2(2-)), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets.

Submerged liquid plasma for the synchronized reduction and functionalization of graphene oxide.

Formation of reduced and functionalized graphene oxide (r-FGO) at ambient temperature and pressure is demonstrated by generating liquid plasma submerged in acetonitrile and graphene oxide solution. The partial restoration of conjugation (sp(2) domain) and insertion of fluorophores such as nitrile and amine in r-FGO displays enhanced fluorescence property. Presence of nitrile and amine in r-FGO are confirmed by X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy. Morphology and optical property of r-FGO are studied with transmission electron microscopy, scanning tunneling microscopy and Ultraviolet-visible spectroscopy measurements. The nitrile and amine present in r-FGO undergo a surface-controlled reversible redox reaction and sp(2)- enriched r-FGO acts as an electrical double layer, providing additional hybrid capacitance or pseudocapacitance. r-FGO shows high cyclic stability with a specific capacitance value of 349 F/g at the scan rate of 10 mV/s. Only marginal reduction of specific capacitance (<10% reduction) is observed at the end of 1000 cycles.