Ion transport in sulfonated nanoporous colloidal films.

The surface of self-assembled nanoporous silica colloidal crystalline films comprised of 184-nm-diameter silica spheres has been sulfonated using 1,3-propanesultone. The transport of ions through the sulfonated films has been studied using cyclic voltammetry in water as a function of ion charge, pH, and solution ionic strength. We found that the flux of anions through the sulfonated colloidal films is reduced, while the flux of cations is increased, compared to the unmodified colloidal films. This behavior is pH-dependent and is due to electrostatic repulsion/attraction that can be modulated by changing the ionic strength of the contacting solution.