Dispersion and stability of titanium dioxide nanoparticles in aqueous suspension: effects of ultrasonication and concentration

The increasing applications of titanium dioxide (TiO₂) nanoparticles raise concerns about their potential environmental impacts. To investigate the fate and transport of TiO₂ nanoparticles in aqueous suspension, ultrasonication is widely used for the dispersion of TiO₂ nanoparticles in laboratory-scale studies. There is a pressing need for detailed information on the dispersion and stability of TiO₂ nanoparticles. This study investigated the change of size, zeta potential, and pH of TiO₂ nanoparticles aqueous suspension under different conditions of ultrasonication and concentrations. It was found that the hydrodynamic diameter of TiO₂ nanoparticles decreased with increasing suspension concentration and remained stable for more than 1 hour after sonication, which is enough for experimental research. The pH decreased with increasing nanoparticles concentration. Ultrasonication remarkably improved zeta potential to be above 15 mV for all the samples. Therefore, 20 minutes of ultrasonication (180 W) is sufficient for the dispersion of this rutile TiO₂ nanoparticles suspension, which can remain stable for more than 1 hour. However, the optimum sonication time for TiO₂ nanoparticles dispersion is influenced by many factors, such as TiO₂ nanoparticles concentration, solution chemistry, and sonicator parameters.