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Posted: Dec 14, 2010
Hollow capsules expand graphene nano-toolbox
(Nanowerk Spotlight) Graphene has attracted a huge amount of attention in recent years with its extraordinarily high electrical and thermal conductivities, mechanical, chemical properties, and large surface area. In order to meet the various demands for a variety of applications, preparation of desired structures of graphene sheets with controlled dimension and architecture are of significant importance. For example, a number of approaches have been made to assemble well-dispersed oxidized or chemically reduced graphene oxide nanosheets into thin films with tailorable properties. Researchers even have made the surprising finding that graphene-based nanomaterials possess excellent antibacterial properties and fabricated antibacterial paper made from graphene.
While research on flat graphene oxide structures – papers and membranes, transparent conducting electrodes, hybrid thin films – has become quite common, there have been few reports on the preparation of hollow capsules of graphene through the nanosize, controlled assembly of graphene.
Researchers in South Korea have now demonstrated the formation of graphene-based capsules through layer-by-layer (LbL) assembly of surface-functionalized reduced graphene oxide nanosheets of opposite charges onto polystyrene colloidal particles to produce multilayer thin films of graphene nanosheets.
The LbL assembly technique offers a variety of opportunities to prepare multilayer films of desired functions with a nanometer scale control over the composition and thickness. In addition, LbL assembly enables preparation of conformal thin films onto virtually any substrate, irrespective of its size and shape, further expanding its potential in creating three-dimensional objects beyond the traditional thin films on a two-dimensional surface.
"By taking advantage of versatile nano-size control assembly, we have demonstrated the successful formation of three-dimensional hollow graphene oxide capsules," Byeong-Su Kim tells Nanowerk. "We anticipate that the results presented in our study will provide a basis for designing various hollow graphene structures to open new possibilities in catalysis, porous graphene membranes, drug delivery, and electrochemistry."
Schematic illustration of a) the LbL assembly of reduced graphene oxide nanosheets onto polystyrene colloidal particles and b) the preparation of reduced graphene oxide nanosheet multilayered hollow capsules with removal of the sacrificial template. (Reprinted with permission from American Chemical Society)
Kim's team prepared positively and negatively charged graphene oxide sheets which they then layered onto a colloidal polystyrene particle based on the electrostatic interactions of the positively and negatively charged sheets. After removing the sacrificial colloidal template by THF treatment, they were left with hollow graphene oxide capsules.
"We expanded this approach in incorporating a new functionality such as gold nanoparticles into the shell of hollow graphene capsule," Kim points out. "Considering the broad range of potential applications of graphene sheets, our approach may lead to new possibilities for the fabrication of novel graphene structures endowed with multiple functionalities. We believe this hollow-shell graphene capsule would have a potential impact on the drug delivery, catalytic vehicles and many more."