We report the synthesis of ultra-low-density three-dimensional macroassemblies of graphene sheets that exhibit high electrical conductivities and large internal surface areas. These materials are prepared as monolithic solids from suspensions of single-layer graphene oxide in which organic sol-gel chemistry is used to cross-link the individual sheets. The resulting gels are supercritically dried and then thermally reduced to yield graphene aerogels with densities approaching 10 mg/cm(3). In contrast to methods that utilize physical cross-links between GO, this approach provides covalent carbon bonding between the graphene sheets. These graphene aerogels exhibit an improvement in bulk electrical conductivity of more than 2 orders of magnitude (∼1 × 10(2) S/m) compared to graphene assemblies with physical cross-links alone (∼5 × 10(-1) S/m). The graphene aerogels also possess large surface areas (584 m(2)/g) and pore volumes (2.96 cm(3)/g), making these materials viable candidates for use in energy storage, catalysis, and sensing applications.

Nearly monodisperse hollow gold nanospheres (HGNs) with tunable interior and exterior diameters have been synthesized by sacrificial galvanic replacement of cobalt nanoparticles. It is possible to tune the peak of the surface plasmon band absorption between 550 and 820 nm by carefully controlling particle size and wall thickness. Cobalt particle size is tunable by simultaneously changing the concentration of sodium borohydride and sodium citrate, the reducing and capping agent, respectively. The thickness of the gold shell can be varied by carefully controlling the addition of gold salt. With successful demonstration of ensemble as well as single HGN surface-enhanced Raman scattering, these HGNs have shown great potential for chemical and biological sensing applications, especially those requiring nanostructures with near-IR absorption.

Laser-induced phototherapy is a new therapeutic use of electromagnetic radiation for cancer treatment. The use of targeted plasmonic gold nanoparticles can reduce the laser energy necessary for selective tumor cell destruction.

Developing three-dimensional (3D) graphene assemblies with properties similar to those individual graphene sheets is a promising strategy for graphene-based electrodes. Typically, the synthesis of 3D graphene assemblies relies on van der Waals forces for holding the graphene sheets together, resulting in bulk properties that do not reflect those reported for individual graphene sheets. Here, we report the use of sol-gel chemistry to introduce chemical bonding between the graphene sheets and control the bulk properties of graphene-based aerogels. Adjusting synthetic parameters allows a wide range of control over surface area, pore volume, and pore size, as well as the nature of the chemical cross-links (sp(2) vs sp(3)). The bulk properties of the graphene-based aerogels represent a significant step toward realizing the properties of individual graphene sheets in a 3D assembly with surface areas approaching the theoretical value of an individual sheet.