Controlling nanocrystal density and location on carbon nanotube templates

We have demonstrated a covalent route toward site-selective synthesis of MWNT - nanoparticle conjugates containing two different types of nanoscale species, i.e., Au nanoparticles and CdSe QDs. We have quantitatively probed the effects of varying oxidation treatments, precursor concentrations, and incubation times in order to rationally affect the spatial coverage and distribution of either Au NPs or semiconducting QDs on the MWNT sidewalls and tips. The degree of nanoparticulate coverage was found to primarily vary with the intensity of the oxidation treatment, though the hydrophobicity of the nanotube as well as the chemical and steric characteristics of the nanocrystals also played a role in determining the ultimate architecture. In general, the stronger the oxidation treatment, the denser the coating of nanoparticles and/or quantum dots on the nanotube surface. In addition, the use of larger concentrations of precursor nanocrystals along with longer incubation times was conducive to the observation of higher nanoparticle densities on our nanotube templates. Interesting charge transfer, electromagnetic enhancement, and energy-transfer behavior between CNTs and the corresponding nanoparticles/ quantum dots have been observed and will likely render such conjugates as key components in a range of nanoscale devices important for photocatalytic and solar applications.