Few-layer-graphene with high yield and low sheet resistance via mild oxidation of natural graphite

Abstract

The mild oxidation of natural graphite was obtained via the modified Hummers method by employing an oxidation temperature of 20 C and KMnO 4 loading of 2 g, while the degree of mild oxidation was controlled by varying the oxidation time from 30 to 60, 90 or 120 min. The mild oxidation of graphite was demonstrated by X-ray diffraction (XRD), along with UV-vis spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Then, MOG (mildly-oxidized graphite)was grafted with aryldiazonium salts of sulfonic acid (ADS) to afford good water dispersion, followed by sonication exfoliation and centrifugation to isolate the few-layer-graphene (FLG). The FLG was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy, and its sheet resistance (R s ), yield and water dispersion stability were also evaluated. The obtained FLG had low R s (3 Â 10 2 to 5.8 Â 10 4 U , À1 ), high yield (19-85%), and good stability in water (79-86% after 4 week aging).

Millstone Exfoliation: a True Shear Exfoliation for Large-Size Few-Layer Graphene Oxide

“…However, the lower absorption with MOG-90 can be explained by the damaged sp 2 carbon bonds resulting from a high degree of oxidation, despite the higher degree of exfoliation, since the damaged sp 2 carbon bond does not contribute to the UV-vis absorption. This trend is similar to what was reported for the sonication exfoliation of MOG solution [ 41 ].…”

“…Mildly oxidized graphite (MOG) solutions prepared by the modified Hummers method provided UV-vis absorptions of 7.8, 9.9, and 11.2 for MOG-30, MOG-60, and MOG-90, respectively (these are slightly higher than the values from the previous study [ 41 ] since they were measured at 660 nm rather than at 750 nm), indicating mild oxidation. As expected from the previous study [ 41 ], there was a high degree of oxidation-exfoliation, but fairly thick MOG plates with some edge-expanded MOG were observed from all samples, demonstrating that mild oxidation took place (Additional file 1 : Figure S1). SEM micrographs after ADS grafting showed fairly thin (~ 1 μm) MOG plates (Fig.…”

“…This is attributed to FLGO with damaged sp 2 carbon bonds, which can contribute to the weight but not to the UV-vis absorption. When compared with 19, 55, and 73% yield obtained from sonication exfoliation [ 41 ], one can see that the yield is higher, similar, or lower for MOG-30, MOG-60, or MOG-90, respectively. The higher yield with MOG-30 can be attributed to true shear exfoliation, which is much less affected by the degree of oxidation than sonication exfoliation.…”

“…Mildly oxidized natural graphite (MOG) was prepared via the modified Hummers method, as published earlier [ 41 ], and used for MS exfoliation to afford few-layer graphene oxide (FLGO) with good property and high yield. A brief description of the preparation of MOG is as follows: After charging 46 ml of H 2 SO 4 into a round bottom flask in a 20 °C water bath, 2 g of natural graphite was added, followed by the slow addition of 4 g of KMnO 4 .…”

“…In this study, therefore, a new millstone-based device was introduced for the exfoliation of GTO, in an effort to minimize fragmentation and produce large-size FLGO. In addition, mildly oxidized graphite (MOG) was employed to afford FLGO with both good property and high yield, as reported previously [ 41 ].…”