Dominating Role of Ionic Strength in the Sedimentation of Nano-TiO2 in Aquatic Environments

Various factors affect the sedimentation behavior of nanotitanium dioxide (n-TiO 2 ) in water. Accordingly, this study aimed to select the dominating factor. An index of sedimentation efficiency related to n-TiO 2 concentration was applied to precisely describe the n-TiO 2 sedimentation behavior. Ionic strength (IS), natural organic matter (NOM) content, and pH were evaluated in sedimentation experiments. An orthogonal experimental design was used to sequence the affecting ability of these factors. Furthermore, simulative sedimentation experiments were performed. The n-TiO 2 sedimentation behavior was only affected by pH and NOM content at low levels of IS. Moreover, divalent cations can efficiently influence the n-TiO 2 sedimentation behavior compared with monovalent cations at fixed IS. Seven different environmental water samples were also used to investigate the n-TiO 2 sedimentation behavior in aquatic environments. Results confirmed that IS, in which divalent cations may play an important role, was the dominating factor influencing the n-TiO 2 sedimentation behavior in aquatic environments.