COVALENT NANOTUBE FUNCTIONALIZATION
Click Coupling to SWNTs

This work involves the functionalization of SWNTs with terminal alkyne groups, allowing for Cu(I)-catalyzed "click" coupling to azide-terminated polymers. This high-yielding coupling reaction enables covalent attachment of a variety of small molecules and polymers to the nanotube surface. Attachment of narrow-polydispersity azide-terminated polystyrene resulted in increased solubility of the nanotube-polymer complex in organic solvents. Current efforts include the introduction of functional polymers, capable of serving as polymeric linkers for nanotubes with other nano-structured materials. The general and orthogonal nature of the click coupling reaction enables the study of structure-activity relationships, including the effect of molecular weight and polymer architecture on solubility and self-assembly properties.

Key Reference: J. Am. Chem. Soc., 2005, 127, 14518-14524.
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Radical Coupling to SWNTs

The combination of single-walled carbon nanotubes (SWNTs) with metal nanoparticles has been an area of recent interest due to the attractive electronic, mechanical, catalytic, and photonic properties of such materials. We have developed a simple method for the production of carbon nanotube thin films containing Au nanoparticles. SWNTs functionalized with highly branched poly(ethylene imine) (Mn = 10 kDa) were prepared as shown above, and were found to exhibit impressive aqueous solubility (180 mg/L), allowing for the formation of homogeneous thin films by vacuum filtration. These films were subsequently functionalized with Au nanoparticle clusters by in-situ reduction of HAuCl4 under mild conditions in the absence of additional reducing agents. Incubating these films in aqueous HAuCl4 solutions resulted in a high density, uniform distribution of Au nanoparticle clusters along the film surface, which could be imaged by TEM (see below).

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PEI functionalized carbon nanotube thin films, decorated with Au nanoparticles, were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films, which provided a flexible substrate for the nanowires. We showed that the NWs exhibited high optical quality and, if prepared with a core-shell pn-junction structure, rectifying asymmetric current-voltage behaviour was observed. We then produced a working, flexible photovoltaic device from the nanotube-supported nanowires, demonstrating that such hybrid nanostructured constructs could indeed be utilized in working devices.

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