Graphene-wrapped sulfur particles as a rechargeable lithium-sulfur battery cathode material with high capacity and cycling stability.

We report the synthesis of a graphene-sulfur composite material by wrapping poly(ethylene glycol) (PEG) coated submicrometer sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates, and rendering the sulfur particles electrically conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ∼600 mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.

Mn3O4-graphene hybrid as a high-capacity anode material for lithium ion batteries.

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.

Nanocrystal growth on graphene with various degrees of oxidation.

We show a general two-step method for growing hydroxide and oxide nanocrystals of the iron family elements (Ni, Co, Fe) on graphene with two degrees of oxidation. Drastically different nanocrystal growth behaviors were observed on low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in hydrothermal reactions. Small particles precoated on GS with few oxygen-containing surface groups diffused and recrystallized into single-crystalline Ni(OH)(2) hexagonal nanoplates or Fe(2)O(3) nanorods with well-defined morphologies.

A route to brightly fluorescent carbon nanotubes for near-infrared imaging in mice.

The near-infrared photoluminescence intrinsic to semiconducting single-walled carbon nanotubes is ideal for biological imaging owing to the low autofluorescence and deep tissue penetration in the near-infrared region beyond 1 microm. However, biocompatible single-walled carbon nanotubes with high quantum yield have been elusive. Here, we show that sonicating single-walled carbon nanotubes with sodium cholate, followed by surfactant exchange to form phospholipid-polyethylene glycol coated nanotubes, produces in vivo imaging agents that are both bright and biocompatible.

Solvothermal reduction of chemically exfoliated graphene sheets.

We have developed a solvothermal reduction method that affords more effective reduction of chemically derived graphene sheets and graphite oxide than low-temperature reduction methods. Solvothermal reduction removed oxygen and defects from graphene sheets, increased the size of sp(2) domains, and produced materials that were as conducting as pristine graphene and exhibited clear intrinsic Dirac behavior.

Nano-Graphene Oxide for Cellular Imaging and Drug Delivery.

Two-dimensional graphene offers interesting electronic, thermal, and mechanical properties that are currently being explored for advanced electronics, membranes, and composites. Here we synthesize and explore the biological applications of nano-graphene oxide (NGO), i.e.