Laser-Induced Synthesis of Pure Zinc Oxide Nanoflakes

Abstract

Nanostructured zinc oxide (ZnO) has received immense attention as a low-cost and non-toxic photo-active material for different applications such as photocatalysis, photovoltaics, photonic and bio-medical fields. Herein, facile crystalline ZnO nanoflakes were prepared by homogeneous precipitation followed by laser-induced recrystallization and without the use of any organic ligand. The effect of laser type and wavelength on the recrystallization process was studied adopting a pulsed nitrogen laser (λ=337 nm) and a continuous argon laser (λ=488 nm). The pulsed nitrogen laser features a pulse duration of 150±1 ns, pulse energy of 1.3±0.3 mJ, and a target irradiance of 5.7±0.5 kW/cm2 while the continuous argon laser provides an irradiance of 10±0.3 mW/cm2. The morphology, structure and optical properties of the prepared nanostructures were studied using a scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Visible, photoluminescence (PL), and Raman spectroscopy. The results confirm the formation of pure ZnO nanoflakes of the wurtzite structure. The laser-induced evolution of ZnO nanoflakes depends on the nature of the precipitating agent, laser energy and exposure time. The ZnO nanoflakes prepared using urea-assisted homogeneous precipitation is more advantageous than that precipitated with NaOH. Moreover, the pulsed nitrogen laser of higher irradiance demonstrated an enhanced formation of ZnO nanoflakes after 90 min of irradiation. The laser irradiation provides a facile synthetic route to pure ZnO nanostructures for various applications.