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 s 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.