Dissolution kinetics of titanium dioxide nanoparticles: the observation of an unusual kinetic size effect.

Different types of industrially produced titanium dioxide nanoparticles and a precipitated titanium dioxide have been dissolved in aqueous NaCl solutions at temperatures of 25 and 37 degrees C. The titanium concentration in solution with regard to dependence on time has been determined up to 3000 h after starting the dissolution experiment. The effect of particle size, pH value, temperature, background electrolyte concentration, and mass concentration of titanium dioxide exposed to the liquid phase has been studied. The nanoparticles have been characterized by N2 physisorption measurements and XRD. The total dissolved titanium in solution has been determined by adsorptive stripping voltammetry (AdSV) and inductively coupled plasma mass spectrometry (ICP-MS). A new kinetic size effect has been observed. It turns out that this effect can be explained by applying an already existing phenomenological thermodynamic and kinetic model. The model describes all possible phenomena in a colloidal dispersion, nucleation, growth of particles, Ostwald ripening, and dissolution of particles using a uniform concept.