We investigate the effects of a foreign substance, silica (SiO2), on surface chemistry of commercial titania (TiO2) nanopowder and its chemical interactions with dispersants. The surface of as-received TiO2 is covered with a 2-3-nm-thick layer of SiO2, which gives the nanopowder a low isoelectric point and makes it acidic. Treating the surface with an acidic solution thins the SiO2 layer to less than 0.5 nm, which allows the TiO2 nanoparticles to exhibit surface properties similar to uncoated TiO2 nanoparticles. This variation of surface property of TiO2 due to acid-treatments results in a great impact on its interactions with dispersants. For as-received TiO2 nanoparticles, no competitive adsorption is observed between the acidic dispersant, oleic acid (OA), and the alkaline dispersant, oleylamine (OLA). However, for acid-treated TiO2 nanoparticles, OA competes readily with the adsorption of OLA (C) 2011 Elsevier B.V. All rights reserved.