COVALENT NANOTUBE FUNCTIONALIZATION
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.
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).
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.
