SIZE DEPENDENCE OF THE DISSOLUTION OF ZNO NANOPARTICLES

ZnO nanoparticles of about 30-60 Angstrom size in ethanolic solution w ere etched by addition of anhydrous acetic acid. Upon dissolution, the volume-weighted particle size decreased by about 10%. The polydispers ity increased slightly. The dissolution rate was strongly dependent on particle size, and size selective etching of a mixture of ZnO particl es was demonstrated. The change of the particle size during etching ca n be modeled adequately by a Monte Carlo simulation, in which the know n degree of polydispersity and the size dependence of the etch rate ar e taken into account. On the basis of a comparison with work on the di ssolution of silica nanoparticles and oxidic thin films, and on the et ching of single-crystal ZnO, it is proposed that the size dependence i s caused by variations of the chemical reactivity of the nanoparticles related to, for example, the concentration of defects and kink sites. Thus, dissolution provides a convenient method to investigate size-de pendent chemical properties.