Synthesis, formation and growth of zinc oxide followed by UV-Vis and SAXs measurements

Full text: Zinc Oxide is one of the most versatile and therefore extensively studied metal oxide semiconductors having several applications as UV blockers, sensors, and photocatalysts. Further interest in ZnO arises due to its multifunctional properties like large exciton binding energy (60meV) coupled with a direct wide band gap (Eg ∼3.37 eV) which makes it thermally stable at room temperature [1]. Since the discovery of quantum size effect in ZnO, the conventional optical spectroscopy became a popular method to study the size dependent shifts in the optical absorption in growing ZnO nanocolloids. Elucidating the earliest stages of ZnO growth is the key to understanding the mechanism which governs the formation of nanostructures. The origin and destiny of the 'primary particle', how and where the nucleation and growth start and terminate, all this belongs to central questions approached in current fundamental studies and applied nanomaterials engineering [2]. In this work the preparation of ZnO sol was based on the method proposed by Spanhel and Anderson [3].The zinc organometallic precursor (Zn₄ O(CH₃COO)₆) was prepared from zinc acetate dissolved in absolute ethanol. The solution, 0.05 mol L^-1 of Zn⁺², was placed into a reflux apparatus for 3 h at 80 deg C. After that, the condensate was cooled at -5 deg C and submitted to hydrolysis by using LiOH ([OH^-2]/[Zn⁺²] = 0.4). The UV-vis absorption spectra of zinc oxide colloidal suspension were followed by using a Cary 500 Scan spectrophotometer and the small-angle X-ray scattering (SAXS) measurements performed at LNLS in Campinas. References: [1] Ü. Özgür et al. A comprehensive review of ZnO materials and devices. J. Appl. Phys. V.98, p.1-103, 2005. [2] Spanhel, L. Colloidal ZnO nanostructures and functional coatings: A survey. J. Sol-Gel Sci. Technol. v.39, p.7-24, 2006. [3] Spanhel, L.; Anderson, M. A. Synthesis and Growth of ZnO Nanoparticles. J.Am.Chem. Soc.v.113, p.2826-2823, 1991. (author)