An Approach for Ultrafast Growth of Zinc Oxide Nanorods via Microwave Irradiation

Abstract

A sealed-vessel approach produced high-purity wurtzite hexagonal ZnO nanorods (P63mc, JCPDS 00-36-1451) with an exceptionally rapid holding duration of 50 sec at 150°C, utilizing microwave radiation from a Monowave 400 reactor. The process is more rapid than prior microwave methods, which require 2-7 min, and is significantly quicker than hydrothermal and sol-gel techniques that take hours to days, utilizing less than 10 Wh of energy compared to the energy-intensive hydrothermal method (energy savings exceeding 95%). The XRD study indicated a Scherrer crystallite size of 25.22 nm, a crystallinity of 48.5%, and a microstrain, as per the Williamson-Hall equation, of ε × 10³ = 3.39. The results are consistent with a highly organized hexagonal wurtzite structure characterized by cell parameters a = b = 3.2494 Å and c = 5.2066 Å. A TEM study of 100 nanorods revealed a uniform morphology with an average diameter of 22.4 ± 3.2 nm, a length of 185 ± 25 nm, and an aspect ratio of 8.3 ± 1.4, indicating preferential development along the c-axis attributable to microwave coupling. The UV-Vis spectrophotometer yielded a cutoff absorption wavelength of λ = 374 nm, which corresponds to a band gap energy of 3.318 eV. The Fourier transformed infrared (FTIR) spectra validated the lattice vibrations of Zn-O bonds at 436 and 630 cm⁻¹. Energy dispersive X-ray (EDX) revealed a near-stoichiometric composition (Zn = 51.48% and O = 48.52%), with no detected contaminants.