Related Experiment Video
Updated: Jul 20, 2026

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles
Published on: March 2, 2016
Stability and electrostatics of mercaptoundecanoic acid-capped gold nanoparticles with varying counterion size
Timo Laaksonen1, Päivi Ahonen, Christoffer Johans
1Laboratory of Physical Chemistry and Electrochemistry Helsinki University of Technology, P.O. Box 6100, 02015 HUT, Finland.
Abstract:
The solubility of charged nanoparticles is critically dependent on pH. However, the concentration range available with bases such as NaOH is quite narrow, since the particles precipitate due to compression of the electric double layer when the ionic strength is increased. The stability of mercaptoundecanoic acid-capped Au nanoparticles is studied at a set pH using the hydroxide as base and different cations of various sizes. The counterions used are sodium (Na(+)), tetramethylammonium (TMA(+)), tetraethylammonium (TEA(+)), and tetrabutylammonium (TBA(+)). The particles precipitate in the 70-90 mM range with Na(+) as the counterion, but with quaternary ammonium hydroxides the particles are stable even in concentrations exceeding 1 M. The change in solubility is linked to a strongly adsorbed layer on the surface of the ligand shell of the nanoparticles. The increased concentration range obtained with TEAOH is further used to facilitate thiol exchange which occurs at a greater extent than would be achieved in NaOH solution.
Related Concept Videos
Complexation Equilibria: Factors Influencing Stability of Complexes
Formation of Complex Ions
Colloidal precipitates
Extraction: Advanced Methods

