Ion transfer at polarised liquid-liquid interfaces modified with adsorbed silica nanoparticles

The interface between two immiscible electrolyte solutions (ITIES) can act as a scaffold for the assembly of nanometer-sized objects. Here we followed the adsorption of silica nanoparticles of 12 nm diameter at the ITIES by AC voltammetry and their interactions with methylene blue (MB+), selected as a model ion, by cyclic voltammetry and UV-vis absorption spectroscopy. We determined the association constant, Kadsaq, of adsorption of MB+ onto silica nanoparticles to be 1.66 105, which indicated a strong affinity between them. This strong affinity shifted the Gibbs free energy of transfer by −8.9 kJ mol−1. This is in contrast with the other two ions investigated (Eosin B and tetraethylammonium), which demonstrated low affinity for the silica nanoparticles. By combining the ability of silica to adsorb onto the ITIES and their affinity for MB+, we were able to accumulate MB+ at the ITIES.