We developed nanosized, reduced graphene oxide (nano-rGO) sheets with high near-infrared (NIR) light absorbance and biocompatibility for potential photothermal therapy. The single-layered nano-rGO sheets were ∼20 nm in average lateral dimension, functionalized noncovalently by amphiphilic PEGylated polymer chains to render stability in biological solutions and exhibited 6-fold higher NIR absorption than nonreduced, covalently PEGylated nano-GO. Attaching a targeting peptide bearing the Arg-Gly-Asp (RGD) motif to nano-rGO afforded selective cellular uptake in U87MG cancer cells and highly effective photoablation of cells in vitro. In the absence of any NIR irradiation, nano-rGO exhibited little toxicity in vitro at concentrations well above the doses needed for photothermal heating. This work established nano-rGO as a novel photothermal agent due to its small size, high photothermal efficiency, and low cost as compared to other NIR photothermal agents including gold nanomaterials and carbon nanotubes.

Ni(OH)(2) nanocrystals grown on graphene sheets with various degrees of oxidation are investigated as electrochemical pseudocapacitor materials for potential energy storage applications. Single-crystalline Ni(OH)(2) hexagonal nanoplates directly grown on lightly oxidized, electrically conducting graphene sheets (GS) exhibit a high specific capacitance of approximately 1335 F/g at a charge and discharge current density of 2.8 A/g and approximately 953 F/g at 45.7 A/g with excellent cycling ability. The high specific capacitance and remarkable rate capability are promising for applications in supercapacitors with both high energy and power densities. A simple physical mixture of pre-synthesized Ni(OH)(2) nanoplates and graphene sheets shows lower specific capacitance, highlighting the importance of direct growth of nanomaterials on graphene to impart intimate interactions and efficient charge transport between the active nanomaterials and the conducting graphene network. Single-crystalline Ni(OH)(2) nanoplates directly grown on graphene sheets also significantly outperform small Ni(OH)(2) nanoparticles grown on heavily oxidized, electrically insulating graphite oxide (GO), suggesting that the electrochemical performance of these composites is dependent on the quality of graphene substrates and the morphology and crystallinity of the nanomaterials grown on top. These results suggest the importance of rational design and synthesis of graphene-based nanocomposite materials for high-performance energy applications.

We developed two-step solution-phase reactions to form hybrid materials of Mn(3)O(4) nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Selective growth of Mn(3)O(4) nanoparticles on RGO sheets, in contrast to free particle growth in solution, allowed for the electrically insulating Mn(3)O(4) nanoparticles to be wired up to a current collector through the underlying conducting graphene network. The Mn(3)O(4) nanoparticles formed on RGO show a high specific capacity up to ∼900 mAh/g, near their theoretical capacity, with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn(3)O(4) nanoparticles grown atop. The Mn(3)O(4)/RGO hybrid could be a promising candidate material for a high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for the design and synthesis of battery electrodes based on highly insulating materials.

A graphene/TiO 2 nanocrystals hybrid has been successfully prepared by directly growing TiO 2 nanocrystals on graphene oxide (GO) sheets. The direct growth of the nanocrystals on GO sheets was achieved by a two-step method, in which TiO 2 was first coated on GO sheets by hydrolysis and crystallized into anatase nanocrystals by hydrothermal treatment in the second step. Slow hydrolysis induced by the use of EtOH/H 2 O mixed solvent and addition of H 2 SO 4 facilitates the selective growth of TiO 2 on GO and suppresses growth of free TiO 2 in solution. The method offers easy access to the GO/TiO 2 nanocrystals hybrid with a uniform coating and strong interactions between TiO 2 and the underlying GO sheets. The strong coupling gives advanced hybrid materials with various applications including photocatalysis. The prepared graphene/TiO 2 nanocrystals hybrid has superior photocatalytic activity to other TiO 2 materials in the degradation of rhodamine B, showing an impressive three-fold photocatalytic enhancement over P25. It is expected that the hybrid material could also be promising for various other applications including lithium ion batteries, where strong electrical coupling to TiO 2 nanoparticles is essential. KEYWORDSGraphene, titanium oxide, photocatalyst, hydrolysis Its interesting electrical and mechanical properties, and high surface area make graphene a novel substrate for forming hybrid structures with a variety of nanomaterials [1][2][3]. Graphene hybrids with metal oxides, metals and polymers have been developed recently for various applications [4][5][6]. Nanocrystal growth on graphene sheets is an important approach to produce nanohybrids, since controlled nucleation and growth affords optimal chemical interactions and bonding between nanocrystals and graphene sheets, leading to very strong electrical and mechanical coupling within the hybrid. Several methods have been proposed to form nanocrystals on graphene sheets, such as electrochemical deposition [7], sol-gel process [8] and gas phase deposition [9,10]. Recently, we developed a controlled, two-step solution phase synthesis of nanocrystals of Ni, Fe, and Co hydroxides or oxides on graphene sheets, which is highly selective in that there is no growth of free nanocrystals in solution [1]. We demonstrated the excellent performance of nickel hydroxide nanoplates grown on graphene for electrochemical pseudocapacitive energy storage, utilizing Nano Res. 2010, 3(10): 701-705

The performance of polymer electrolyte membrane fuel cells is limited by the reduction at the cathode of various oxygenated intermediates in the four-electron pathway of the oxygen reduction reaction. Here we use ambient pressure X-ray photoelectron spectroscopy, and directly probe the correlation between the adsorbed species on the surface and the electrochemical potential. We demonstrate that, during the oxygen reduction reaction, hydroxyl intermediates on the cathode surface occur in several configurations with significantly different structures and reactivities. In particular, we find that near the opencircuit potential, non-hydrated hydroxyl is the dominant surface species. On the basis of density functional theory calculations, we show that the removal of hydration enhances the reactivity of oxygen species. Tuning the hydration of hydroxyl near the triple phase boundary will be crucial for designing more active fuel cell cathodes.