Aggregation behaviour of TiO2 nanoparticles in natural river water

The purpose of this study was to determine and understand the aggregation behaviour of industrial nanoparticulate TiO2 (NPs) in the river water near a TiO2 production plant. The aggregation was tested in near-reality conditions with industrial NPs and the filtered river water in which they are potentially released. The initial size of TiO2 NPs is around 5 nm. The evolution of the hydrodynamic diameters of the TiO2 aggregates in the presence of added Suwannee River fulvic acid (SRFA) and illite in the filtered river water was measured at pH 8 for at least 30 min with dynamic light scattering and laser diffraction. The experiments performed in the filtered river water allowed the determination of the attachment efficiency coefficients, and the experiments performed under conditions facilitating aggregation (with higher Ca2+ content) were used to understand the potential aggregation processes. When no Ca2+ was added into the river water, the initially aggregated TiO2 did not develop a secondary aggregation in the presence of SRFA and illite. Upon the addition of 2.75 mM Ca2+, TiO2 was shown to heteroaggregate with illite at all tested concentrations. Consequently, in the studied river, the fate of the TiO2 NPs does not seem to be related to that of the clay suspended particles upstream of the plant. However, the behaviours of the TiO2 NPs and the clays are closely linked in the water with higher salt content, which is the case downstream of one of the industrial effluent release points.