Coarsening of metal oxide nanoparticles

In solution phase synthesis of nanoparticles, processes such as coarsening and aggregation can compete with nucleation and growth in modifying the particle size distribution in the system. We show that coarsening of ZnO and ${\mathrm{TiO}}_2$ nanoparticles in solution follows the Lifshitz-Slyozov-Wagner rate law for diffusion controlled coarsening originally derived for colloidal systems with micrometer-sized particles, where the average particle size cubed is proportional to time. The rate constant for growth of ZnO in propanol is in the range ${10}^{-4}–{10}^{-2}{\mathrm{nm}}^3{\mathrm{s}}^{-1}$ and is dependent on the precursor anion and temperature. The coarsening of ${\mathrm{TiO}}_2$ nanoparticles from aqueous Ti(IV) alkoxide solutions is slower due to the low solubility of ${\mathrm{TiO}}_2$ with the rate constant in the range ${10}^{-5}–{10}^{-3}{\mathrm{nm}}^3{\mathrm{s}}^{-1}$ for temperatures between 150 °C and 220 °C. Epitaxial attachment of ${\mathrm{TiO}}_2$ particles becomes significant at higher temperatures and longer times. We show that the dominant parameters controlling the coarsening kinetics are solvent, precursor salt, and temperature.