Post-ultrasonic irradiation time is important in initiating citrate-coated α-Fe2O3nanorod formation

Abstract

Ultrasonication of solutions of Fe²⁺ and nitrate at room temperature for few minutes (2–5 min) led to the formation of nanoparticles and nanorods of α-Fe₂O₃ upon further incubation for few hours (2–8 h). Lower power (22 W) or less time (2 min) favoured the formation of irregular shaped nanoparticles. Transmission electron microscopy (TEM) images showed that these nanoparticles were the precursors to the nanorod formation. A longer initial ultrasonication as well as a prolonged incubation resulted in longer and larger numbers of nanorods. The nanorods were characterized by dynamic light scattering (DLS), TEM, selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy and zeta potential measurements. While continuous ultrasonication has been known to assist in the formation of nanomaterials, the use of low power (22 W–44 W) ultrasonication for a limited time period (2 min–5 min) to trigger the subsequent formation of nanostructured materials does not seem to have been reported. The present work, apart from describing a green method for the ultrasonic assisted formation of nanorods of α-Fe₂O₃, may provide an impetus to further understand the role of ultrasonication in the formation of the nuclei/precursors which ultimately dictate the size and shape of the nanomaterials.