Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.

RECEIVED DATE (automatically inserted by publisher); ayan@iisertvm.ac.in Structural and electronic properties of the all-Si analogue of graphene, silicene have elucidated through DFT calculations. Silicene differs considerably from graphene in being 'chair-type' puckered in each 6-membered ring which leads to ordered ripples across the surface. Binding energies suggest stability for such rippled silicenes and are predicted to behave as a finite gap semi-conductor with electron-hole symmetry quenched. Inter-layer coupling between the silicenes is suggested as the mechanism for the formation of the bulk-Si in it's only known diamond form.Graphene has attracted immense interest in the present decade due to its remarkable chemical, physical, mechanical, electronic and magnetic properties. 1-3 This nanoscale 2-D system provides a wonderful starting material for fabricating materials in the nano dimension. Apart from its novel prospects, the fundamental structural aspects of graphene are also very interesting. 4-5 Though expected to be ideally planar, recent experiments and computations suggest that graphene is not really planar and distinct ripples are observed. 6-8 This is also expected from the Mermin-Wagner theorem predicting that thermal fluctuations should destroy long-range order in 2-D systems and instabilities should appear. This phenomenon is similar to the established Peierls distortion in polyacetylene and other 1-D systems. 9 The all silicon analogue of graphene, silicene has generated recent interest. Silicon nanoribbons have been studied through STM studies and DFT calculations. 10-11 Even though there is an immediate possibility of application of silicene based nano-materials in existing Simicroelectronics, the fundamental structural aspects are yet to be elucidated. In this communication, we report the rich structural and electronic aspects in nanosheets of polysilo-acenes and silicenes based on DFT calculations. In marked contrast to graphene, the ground-state of silicene show large, short-range and periodically ordered ripples even in the absence of thermal fluctuations. This effect is a direct consequence of the puckering distortion in the six-membered rings that leads to a gap opening in silicene, unlike the zero-gap semiconductor like behavior in graphene.

Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics.