An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers' method (KMnO(4), NaNO(3), H(2)SO(4)) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO(3), increasing the amount of KMnO(4), and performing the reaction in a 9:1 mixture of H(2)SO(4)/H(3)PO(4) improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers' method or Hummers' method with additional KMnO(4). Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers' method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers' method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the construction of devices composed of the subsequent CCG.

Graphene, or single-layered graphite, with its high crystallinity and interesting semimetal electronic properties, has emerged as an exciting two-dimensional material showing great promise for the fabrication of nanoscale devices [1][2][3] . Thin, elongated strips of graphene that possess straight edges, termed graphene ribbons, gradually transform from semiconductors to semimetals as their width increases 4-7 , and represent a particularly versatile variety of graphene. Several lithographic 7,8 , chemical 9-11 and synthetic 12 procedures are known to produce microscopic samples of graphene nanoribbons, and one chemical vapour deposition process 13 has successfully produced macroscopic quantities of nanoribbons at 950 6C. Here we describe a simple solution-based oxidative process for producing a nearly 100% yield of nanoribbon structures by lengthwise cutting and unravelling of multiwalled carbon nanotube (MWCNT) side walls. Although oxidative shortening of MWCNTs has previously been achieved 14 , lengthwise cutting is hitherto unreported. Ribbon structures with high water solubility are obtained. Subsequent chemical reduction of the nanoribbons from MWCNTs results in restoration of electrical conductivity. These early results affording nanoribbons could eventually lead to applications in fields of electronics and composite materials where bulk quantities of nanoribbons are required [15][16][17] .We obtained oxidized nanoribbons by suspending MWCNTs in concentrated sulphuric acid followed by treatment with 500 wt% KMnO 4 for 1 h at room temperature (22 uC) and 1 h at 55-70 uC (Methods). After isolation, the resulting nanoribbons were highly soluble in water (12 mg ml 21 ), ethanol and other polar organic solvents. The opening of the nanotubes appears to occur along a line, similar to the 'unzipping' of graphite oxide 18,19 , affording straightedged ribbons. This could occur in a linear longitudinal cut (Fig. 1a) or in a spiralling manner, depending upon the initial site of attack and the chiral angle of the nanotube. Although depicted in Fig. 1a as occurring on the mid-section of the nanotube rather than at one end, the location of the initial attack is not known.The mechanism of opening is based on previous work on the oxidation of alkenes by permanganate in acid. The proposed first step in the process is manganate ester formation (2, Fig. 1b) as the ratedetermining step, and further oxidation is possible to afford the dione (3, Fig. 1b) in the dehydrating medium 20 . Juxtaposition of the buttressing ketones distorts the b,c-alkenes (red in 3), making them more prone to the next attack by permanganate. As the process continues, the buttressing-induced strain on the b,c-alkenes lessens because there is more space for carbonyl projection; however, the bond-angle strain induced by the enlarging hole (or tear if originating from the end of the nanotube) would make the b,c-alkenes (4, Fig. 1b) increasingly reactive. Hence, once an opening has been initiated, its further opening is enhanced relative to an unopened ...

Abstract2D transition metal carbide Ti 3 C 2 T x (T stands for surface termination), the most widely studied MXene, has shown outstanding electrochemical properties and promise for a number of bulk applications. However, electronic properties of individual MXene flakes, which are important for understanding the potential of these materials, remain largely unexplored. Herein, a modified synthetic method is reported for producing high-quality monolayer Ti 3 C 2 T x flakes. Field-effect transistors (FETs) based on monolayer Ti 3 C 2 T x flakes are fabricated and their electronic properties are measured. Individual Ti 3 C 2 T x flakes exhibit a high conductivity of 4600 ± 1100 S cm −1 and fieldeffect electron mobility of 2.6 ± 0.7 cm 2 V −1 s −1 . The resistivity of multilayer Ti 3 C 2 T x films is only one order of magnitude higher than the resistivity of individual flakes, which indicates a surprisingly good electron transport through the surface terminations of different flakes, unlike in many other 2D materials. Finally, the fabricated FETs are used to investigate the environmental stability and kinetics of oxidation of Ti 3 C 2 T x flakes in humid air. The high-quality Ti 3 C 2 T x flakes are reasonably stable and remain highly conductive even after their exposure to air for more than 24 h. It is demonstrated that after the initial exponential decay the conductivity of Ti 3 C 2 T x flakes linearly decreases with time, which is consistent with their edge oxidation. A l h a b e b , e t a l . i n A d v a n c e d E l e c t r o n i c M a t e r i a l s 2 ( 2 0 1 6 digitalcommons.unl.edu L i p a t o v &

An improved method is described for the production of graphene oxide nanoribbons (GONRs) via longitudinal unzipping of multiwalled carbon nanotubes. The method produces GONRs with fewer defects and/or holes on the basal plane, maintains narrow ribbons <100 nm wide, and maximizes the high aspect ratio. Changes in the reaction conditions such as acid content, time, and temperature were investigated. The new, optimized method which introduces a second, weaker acid into the system, improves the selectivity of the oxidative unzipping presumably by in situ protection of the vicinal diols formed on the basal plane of graphene during the oxidation, and thereby prevents their overoxidation and subsequent hole generation. The optimized GONRs exhibit increased electrical conductivity over those chemically reduced nanoribbons produced by previously reported procedures.

Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties. Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase. Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as approximately 2 mg ml(-1), which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations ( approximately 20-30 mg ml(-1)). Transparent, conducting films are produced from these dispersions at 1,000 Omega square(-1) and approximately 80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.

Nanoindentation experiments show that Ti3C2Tx MXenes have a higher elastic modulus than other solution-processed 2D materials.

According to theoretical studies, narrow graphene nanoribbons with atomically precise armchair edges and widths of o2 nm have a bandgap comparable to that in silicon (1.1 eV), which makes them potentially promising for logic applications. Different top-down fabrication approaches typically yield ribbons with width 410 nm and have limited control over their edge structure. Here we demonstrate a novel bottom-up approach that yields gram quantities of high-aspect-ratio graphene nanoribbons, which are only B1 nm wide and have atomically smooth armchair edges. These ribbons are shown to have a large electronic bandgap of B1.3 eV, which is significantly higher than any value reported so far in experimental studies of graphene nanoribbons prepared by top-down approaches. These synthetic ribbons could have lengths of 4100 nm and self-assemble in highly ordered few-micrometer-long 'nanobelts' that can be visualized by conventional microscopy techniques, and potentially used for the fabrication of electronic devices.

Here we demonstrate that graphene nanoribbons (GNRs) free of oxidized surfaces can be prepared in large batches and 100% yield by splitting multiwalled carbon nanotubes (MWCNTs) with potassium vapor. If desired, exfoliation is attainable in a subsequent step using chlorosulfonic acid. The low-defect density of these GNRs is indicated by their electrical conductivity, comparable to that of graphene derived from mechanically exfoliated graphite. The possible origins of directionally selective splitting of MWCNTs have been explored using computer modeling, and plausible explanations for the unique role of potassium were found.