Nanoparticle-nanotube electrostatic interactions in solution: the effect of pH and ionic strength

The effect of pH and ionic strength on the magnitude of electrostatic interactions between like-charged citrate-stabilised gold nanoparticles (AuNP) and multi-walled carbon nanotubes (MWNT) in aqueous suspension has been investigated using a combination of UV-vis spectroscopy, z-potential and transmission electron microscopy analyses. Variation of the electrostatic environment by external stimuli has a marked effect on the inherent surface charge of the two components and, in both cases, the magnitude of electrostatic forces (dot product of the surface potentials of the components) is inversely proportional to the number of AuNP adsorbed onto MWNT, indicating that adsorption of nanoparticles on nanotubes is primarily governed by Coulomb interactions. Using this simple approach, we have been able to demonstrate precise control over the composition and structure of the resulting AuNP-MWNT composite materials.