With the rapid expansion of industrial nanotechnology applications, engineered nanoparticles are being introduced into the environment before the controls on their fate and mobility are fully understood. In this study, we measured the adhesion of TiO 2 nanoparticles onto silica and Fe(III) oxide-coated silica surfaces as a function of pH, nanoparticle concentration, and nanoparticle size. Batch TiO 2 adhesion experiments were conducted at pH3-8 and 0.01M NaClO 4 with TiO 2 concentrations ranging from 10 to 200mg/L. Three TiO 2 size fractions, each containing a range of particle sizes, had initial average diameters of 16, 26, and 50nm. Silica grains, both uncoated and coated with Fe(III) oxide, were used as the geosorbents. The extent of TiO 2 nanoparticle adhesion increased with increasing nanoparticle concentration, and pH exerted a strong effect on the adhesion behavior of the nanoparticles onto the uncoated silica particles. At and below pH5, TiO 2 nanoparticle adhesion increased with increasing pH; at pH6 and above, adhesion occurred independently of pH. In general, the differences in adhesion between the three nanoparticle sizes at a given pH were not large. Within a given size fraction, preferential adhesion of the larger TiO 2 particles was suggested below pH6, and preferential adhesion of the smaller TiO 2 particles was suggested at and above pH6. Experiments with the Fe-coated silica grains were conducted only with the 26nm TiO 2 nanoparticles, and, except at pH6 where we observed significantly enhanced adhesion to the Fe-coated silica relative to the uncoated silica, the extents of nanoparticle adhesion onto the two geosorbents were the same within experimental uncertainty. The similarity in adhesion behaviors onto solids with such different surface chemistries suggests that the properties of the TiO 2 nanoparticles, such as agglomeration, and not of the mineral surfaces, are primarily responsible for governing adhesion.
- Iron oxide coating
- Titanium dioxide nanoparticle
ASJC Scopus subject areas
- Geochemistry and Petrology