Mild sonochemical exfoliation of bromine-intercalated graphite: a new route towards graphene

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br2 into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 $mu$m, corresponding to the grain size of the starting material.Comment: 10 pages 4 figure

Sulfur-Directed Olefin Oxidations: Observation of Divergent Reaction Mechanisms in the Palladium-Mediated Acetoxylation of Unsaturated Thioacetals

The Pd-mediated oxidation of unsaturated thioacetals gives either allyl or vinyl esters, depending on the substrate structure. We report the characterization of a range of sulfur-stabilized palladium intermediates via a combined computational and experimental NMR approach, demonstrating that the oxidation proceeds via two divergent reaction mechanisms. We were also able to synthesize an unusual sigma-bound Pd complex, via acetoxypalladation of an unsaturated dithiane, which was characterized by X-ray crystallography

Electrochemical and photoelectrochemical investigation of new carboxylatobipyridine(bis-bipyridine)ruthenium(II) complexes for dye-sensitized TiO2 electrodes

Methods for the prepn. and purifn. of new carboxylated 2,2'-bipyridine ligands, two of which contain the new anchoring functionality malonate, and a reliable method for the synthesis of the corresponding [Ru(bpy)2(L)](PF6)2 complexes are described. Their suitability for fundamental studies of the processes in wet solar cell applications has been investigated. All complexes show stable voltammograms in acetonitrile soln. and although the complexes were obtained as lithium carboxylate salts, they were sol. in non-polar org. solvents such as dichloromethane, which allowed for good reproducibility in the dye-coating step.The electrochem. and photoelectrochem. properties of dye-TiO2 systems are discussed. The photoelectrochem. properties in monochromatic and white light are related to the attaching group that is varied in the series of complexes: A formally non-conjugated malonate group as anchoring group generally gives similar results to that of a conjugated carboxylic group, the second carboxylate compensating the absence of conjugation. Also, the complexes with malonate as attaching group are more efficient than a complex with a non-conjugated carboxylic group, esp. in the red part of the action spectrum.The redox behavior of the adsorbed complexes is reversible at neg. potentials and quasi-reversible at pos. potentials. The latter feature is esp. interesting since it is possible to electrochem. oxidize the surface-attached ruthenium complexes even at potentials in the mid-bandgap region of the metal oxide film