Influences of anion concentration and valence on dispersion and aggregation of titanium dioxide nanoparticles in aqueous solutions

Dispersion and aggregation of nanoparticles in aqueous solutions are important factors for safe application of nanoparticles. In this study, dispersion and aggregation of nano-TiO₂ in aqueous solutions containing various anions were investigated. The influences of anion concentration and valence on the aggregation size, zeta potential and aggregation kinetics were individually investigated. Results showed that the zeta potential decreased from 19.8 to − 41.4 mV when PO₄^3 − concentration was increased from 0 to 50 mg/L, while the corresponding average size of nano-TiO₂ particles decreased from 613.2 to 540.3 nm. Both SO₄^2 − and NO₃⁻ enhanced aggregation of nano-TiO₂ in solution. As SO₄^2 − concentration was increased from 0 to 500 mg/L, the zeta potential decreased from 19.8 to 1.4 mV, and aggregate sizes increased from 613.2 to 961.3 nm. The trend for NO₃⁻ fluctuation was similar to that for SO₄^2 − although the range of variation for NO₃⁻ was relatively narrow. SO₄^2 − and NO₃⁻ accelerated the aggregation rapidly, while PO₄^3 − did so slowly. These findings facilitate the understanding of aggregation and dispersion mechanisms of nano-TiO₂ in aqueous solutions in the presence of anions of interest.