Synthesis, size and colloidal stability of ZnO nanoparticles in ionic solutions

The formation and colloidal stability of zinc oxide nanoparticles, with a mean size smaller than 5 nm, produced under pulsed laser ablation of a zinc metal target in different liquid environments of NaOH and KOH solutions, is reported. Using the 532 nm harmonic of Nd:YAG laser with 65 mJ/p, ZnO nanoparticles were produced only at low concentrations of NaOH. On the other hand at pH>10 and energies above 100 mJ/pulse, ZnO nanoparticles were produced but not exactly after ablation. The nanoparticle size, aggregation, optical properties and colloidal stability of zinc oxide suspensions (including K⁺ or Na⁺) have been examined to understand the mechanism of dispersion. KOH solution, compared to NaOH solution with the same pH, as an environment for zinc oxide nanoparticles, provided more effective degree of sustained nano-particle dispersion due to electrostatic stabilization and consequjently more colloidal stability. For the ZnO nanoparticles produced at pH>10, the colloid showed high stability. The nanoparticles are characterized by UV/VIS transmission spectrometry, TEM, XRD and FTIR.