Deposition of TiO₂ Nanoparticles onto Silica Measured Using a Quartz Crystal Microbalance with Dissipation Monitoring

Titanium dioxide (TiO₂) nanoparticles introduced into subsurface environments may lead to contamination of drinking water supplies and can act as colloidal carriers for sorbed contaminants. A model laboratory system was used to examine the influence of water chemistry on the physicochemical properties of TiO₂ nanoparticles and their deposition. Deposition rates of TiO₂ particles onto a silica surface were measured over a broad range of solution conditions (pH and ionic strength) using a quartz crystal microbalance with energy dissipation monitoring (QCM-D). Higher particle deposition rates were observed under favorable interaction conditions (i.e., in the presence of attractive electrostatic interactions) in comparison to unfavorable deposition conditions where electrostatic repulsion dominates particle−surface interactions. Nanoparticle sizes were characterized by fluorescence correlation spectroscopy (FCS), dynamic light scattering (DLS), and atomic force microscopy (AFM). These analyses confirmed the nanoscale of the system under study as well as the presence of TiO₂ aggregates in some cases. TiO₂ deposition behavior onto silica measured using QCM-D was generally found to be in qualitative agreement with the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory of colloidal stability.