Scott Gilje

Processable aqueous dispersions of graphene nanosheets

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.

A One-Step, Solvothermal Reduction Method for Producing Reduced Graphene Oxide Dispersions in Organic Solvents

Refluxing graphene oxide (GO) in N-methyl-2-pyrrolidinone (NMP) results in deoxygenation and reduction to yield a stable colloidal dispersion. The solvothermal reduction is accompanied by a color change from light brown to black. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images of the product confirm the presence of single sheets of the solvothermally reduced graphene oxide (SRGO). X-ray photoelectron spectroscopy (XPS) of SRGO indicates a significant increase in intensity of the C=C bond character, while the oxygen content decreases markedly after the reduction is complete. X-ray diffraction analysis of SRGO shows a single broad peak at 26.24 degrees 2theta (3.4 A), confirming the presence of graphitic stacking of reduced sheets. SRGO sheets are redispersible in a variety of organic solvents, which may hold promise as an acceptor material for bulk heterojunction photovoltaic cells, or electromagnetic interference shielding applications.

Photothermal deoxygenation of graphene oxide for patterning and distributed ignition applications.

A xenon discharge tube, such as is used to produce a photographic flash, has been reported to cause the ignition of carbon nanotubes, silicon nanowires, and welding of nanofibers of the conducting polymer polyaniline. In these reactions, the high surface-to-volume ratio of the nanomaterials being irradiated, coupled with the inability of the small structures to efficiently dissipate the absorbed energy, leads to a rapid increase in temperature and subsequent ignition or welding of the materials. Although heating materials through the use of light energy is not a new phenomenon, achieving such a rapid and dramatic temperature change using only millisecond pulses of light demonstrates a tangible and technologically significant capability that is unique to nanoscale materials. Graphene oxide (GO) is a deeply colored, water dispersible, oxidized form of graphene obtained through the treatment of graphite powder with powerful oxidizing agents. Although GO has been known for over 150 years, only recently have scientists had access to the tools necessary to properly analyze its atomically thin sheet structure. This has rekindled interest in graphite oxide and has led to a number of recent discoveries, including: the stacking of GO platelets to form paper-like materials of high modulus and strength. Many studies have suggested that GO can be reduced to graphene-like carbon sheets by applying chemical reducing agents or by using thermal treatments. This has led to speculation that GO could find use as a precursor in a bulk route to dispersible graphene sheets. Already, several groups have succeeded in creating conducting polymer composites, transparent conducting films, and simple electronic devices based on reduced GO. In addition to the chemical reduction of GO, Aksay, et al. have reported the thermal deoxygenation of GO to create functionalized graphene sheets upon rapid heating to 1100 8C under an inert atmosphere. These organic solvent dispersible sheets have enabled the direct creation of polymer composites, without the need for surfactants. Thermal deoxygenation of GO to form graphitic carbon dates back to the 1960s when Boehm and Scholz first reported on the ignition and deflagration of graphite oxides prepared by different methods. Upon rapid heating to temperatures of 200 8C, GO decomposes to the most thermodynamically stable oxide of carbon, CO2. Along with the exothermic release of CO2, H2O, and CO also form as minor products. [31]

Graphene-like nano-Sheets/36° LiTaO 3 surface acoustic wave hydrogen gas sensor

Presented is the material and gas sensing properties of graphene-like nano-sheets deposited on 36deg YX lithium tantalate (LiTaO3) surface acoustic wave (SAW) transducers. The graphene-like nano-sheets were characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The graphenelike nano-sheet/SAW sensors were exposed to different concentrations of hydrogen (H2) gas in a synthetic air at room temperature. The developed sensors exhibit good sensitivity towards low concentrations of H2 in ambient conditions, as well as excellent dynamic performance towards H2 at room temperature.

Semiconducting graphite oxide films for large scale carbon based electronics

Single sheet graphite oxide films are synthesized by intercalation and exfoliation routes of graphite. Those insulating graphite oxide films were deposited on SiO2/Si substrates and reduced to semiconducting graphene. Field effect transistors of these graphite oxide and graphene films were fabricated. The transport properties of the devices were studied before and after the reduction reaction. Such method opens up the possibility of preparing high quality, large area and manufacturable graphene films with low cost.