Au–carbon nanotube composites from self-reduction of Au3+ upon poly(ethylene imine) functionalized SWNT thin films

Abstract

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. Although complexes of SWNTs and nanoparticles are known, macroscopic samples in which nanoparticles are uniformly dispersed in high density throughout the nanotube substrate have not been reported. Here, a simple method for the production of carbon nanotube thin films containing Au nanoparticles is described. SWNTs functionalized with highly branched poly(ethylene imine) (M_n = 10 kDa) were found to exhibit impressive aqueous solubility (180 mg L⁻¹), allowing for the formation of homogeneous thin films by vacuum filtration. These films were subsequently functionalized with Au nanoparticle clusters by in-situreduction of HAuCl₄ under mild conditions in the absence of additional reducing agents. Using thermogravimetric analysis, it was determined that poly(ethylene imine) functionalized SWNTs contained 17 wt% polymer, which amounts to one polymer chain for every 2600 carbon atoms within the nanotubes. Incubating these films in aqueous HAuCl₄ solutions resulted in a high density, uniform distribution of Au nanoparticle clusters along the film surface. In addition, using transmission electron microscopy (TEM) and focused ion beam (FIB) milling within a scanning electron microscope (SEM), nanoparticles were found to be embedded at various depths throughout the film. SEM was employed to determine Au nanoparticle diameter and distribution. The average diameter of the Au clusters could be controlled in the range of 50 to 550 nm.