The influence of anion on the coarsening kinetics of ZnO 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 report on the synthesis of ZnO nanoparticles from Zn(CH3CO2)(2), ZnBr2, and Zn(ClO4)(2) in 2-propanol. For synthesis from Zn(CH3-CO2)(2) and ZnBr2, nucleation and growth are fast and are followed by diffusion-limited coarsening. For synthesis from Zn(ClO4)(2), diffusion-limited coarsening is observed at shorter times whereas at longer times the particle size increases more rapidly. The rate constant for coarsening at constant temperature increases in the order Br- < CH3CO2- < ClO4- indicating that the rate is dependent on anion adsorption. The temperature dependence of the rate constant for coarsening is due to the temperature dependence of the solvent viscosity and the temperature dependence of the bulk solubility of ZnO.