Controlled dispersion of ZnO nanoparticles produced by basic precipitation in solvothermal processes

Abstract

Zinc oxide nanoparticles were successfully synthesized under precipitation processes, using ZnSO₄·7H₂O as a Zn²⁺ precursor and K₂CO₃ used as a basic source, and hydrozincite was obtained as an intermediary, which was treated under two procedures; first procedure involved multiple stages to get final precipitated with NaOH, and in the second procedure the hydrozincite was straightforwardly dried at 220 °C. By both processes ZnO structures were obtained, which were turned into nanoparticles by a solvothermal treatment, for four hours in ethylene glycol at 200 °C. The final products for the first procedure was conglomerate of spherical nanoparticles with sizes ranged between 5-10 nm and dispersed ellipsoidal nanoparticles for the second procedure. Apart off the two procedures mentioned above, another synthesis was carried out with the same Zn²⁺ precursor but now using NaOH, and the solvothermal treatment produced ZnO mixed micro-structures which under ultrasonic cavitation disaggregated on mesoporous ZnO nanoplates of hexagonal shapes with nanopore sizes of approximately 0.35 nm. All ZnOs synthesized were structurally characterized with XRD, TEM and FT-IR techniques, and electronically with UV-Vis absorption and diffuse reflectance spectroscopies.

Keywords: Alkaline media; Precipitation; Solvothermal treatment; Ultrasonic cavitation; Zinc oxide nanoparticles; ZnO mesoporous.