Stability of nano-sized titanium dioxide in an aqueous environment: effects of pH, dissolved organic matter and divalent cations

Nano-sized titanium dioxide in the aquatic environment has a potential impact on the environment and human health. In this study, the impact of pH value, dissolved organic matter (DOM) and divalent cations (Ca²⁺) on the stability of titanium dioxide nanoparticles (nano-TiO₂) in an aqueous environment was investigated in batch tests. The results showed that the particle size of nano-TiO₂ was not sensitive to pH value but was inversely proportional to zeta potential. The nano-TiO₂ becomes more stable with surface zeta potential, accompanied by small particle size and high dispersion. In the presence of DOM, the particle size was smaller and the stability of nano-TiO₂ could be enhanced. This might be a synergistic effect of the ligand exchange and electrostatic force. Particle size increased with the addition of Ca²⁺ and the stability decreased.