Graphene hydrogel/nickel foam composite electrodes for high-rate electrochemical capacitors are produced by reduction of an aqueous dispersion of graphene oxide in a nickel foam (upper half of figure). The micropores of the hydrogel are exposed to the electrolyte so that ions can enter and form electrochemical double-layers. The nickel framework shortens the distances of charge transfer. Therefore, the electrochemical capacitor exhibits highrate performance (see plots).

We report an improved Hummers method for synthesizing graphene quantum dots (GQDs) by directly oxidizing and etching graphite powders. The yield of GQDs is as high as 63 ± 7% (by weight, wt%), suggesting this technique is suitable for producing GQDs on a large scale. The GQDs are nanocrystals with lateral dimensions in the range of 2-4 nm and an average thickness of around 1.3 nm. The emission peaks of as-prepared GQDs can be tuned in the range of 440 to 510 nm by varying the reaction conditions. Their fluorescence quantum yields were tested to be around 1%, which could be further increased to about 3% by hydrothermal treatment. These GQDs have low cytotoxicity and excellent biocompatibility, indicating that they are promising for biological applications.

Gold@carbon dots composite nanoparticles (Au@CDs) with ultrathin carbon dot (CD) shells of ca. 2 nm were prepared by reducing HAuCl(4) with CDs at 100 °C. By adjusting the feeding mass ratio of HAuCl(4) to CDs, the average diameters of Au@CDs can be modulated from 8 to 44 nm. The suspension of Au@CDs with an average diameter of ca. 24 nm was applied as a substrate for surface enhanced Raman scattering (SERS) and it exhibited a higher SERS effect for rhodamine 6G (Rh6G) than the suspension of pure Au nanoparticles with nearly the same size. The excellent SERS effect of Au@CDs is mainly attributed to their improved capability of adsorbing the aromatic probe molecules.

Chemical modification is an important technique to modulate the chemical and optical properties of graphene quantum dots (GQDs). In this paper, we report a versatile diazonium chemistry method to graft aryl groups including phenyl, 4-carboxyphenyl, 4-sulfophenyl and 5-sulfonaphthyl to GQDs via Gomberg-Bachmann reaction. The aryl-modified GQDs are nanocrystals with lateral dimensions in the range of 2-4 nm and an average thickness lower than 1 nm. Upon chemical modification with aryl groups, the photoluminescence (PL) bands of GQDs were tuned in the range of 418 and 447 nm, and their fluorescence quantum yields (QYs) were increased for up to about 6 times. Furthermore, the aryl-modified GQDs exhibited stable PL (both intensity and peak position) in a wide pH window of 1-11. The mechanism of improving the PL properties of GQDs by aryl-modification was also discussed.

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