An investigation on the aggregation phenomena of Titanium dioxide nanoparticles in natural waters: role of ionic strength, and organic matter

摘要

The aggregation of TiO_2 nanoparticles under different aqueous matrixes representative of natural waters was experimentally investigated. Conditions included indiferent electrolytes (NaCl) and specifically adsorbing cations (CaCl_2 and MgCl_2), in the presence and absence of natural organic matter. The nanoparticles of 21 nm primary particle size, formed stable aggregates of aproximately 250 nm under conditions unfavorable for aggregation, while size increased significantly at pHs near or at the pzc of the material (pzc TiO_2 6.3). The pH for favorable aggregation was affected by the presence of divalent cations and natural organic matter, turning the nanoparticles mobile at conditions were otherwise limited mobility should be expected. DLVO calculations confirmed the experimental observations, if the stable aggregate size was applied as the primary size of the particles. Aggregate morphology observed by SEM was in agreement with proposed mechanisms.