Ultrasonic synthesis of α-MnO nanorods: An efficient catalytic conversion of refractory pollutant, methylene blue.

In this work, uniform α-MnO nanorods were synthesized via a simple hydrothermal followed by ultrasonication method using ultrasonic bath (20 kHz, 100 W) without using any surfactant and template. The crystallographic phases and surface morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transition electron microscopy (TEM) analysis, respectively. Functional group identification and chemical states of α-MnO nanorods were confirmed by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The as-synthesized uniform nanorods of α-MnO exhibit excellent catalytic conversion of toxic organic contaminant (methylene blue (MB)) in the presence of NaBH as reductant. The α-MnO exhibits excellent stability up to four repeated catalytic cycles with nearly 92% conversion. The kinetic rate constant (k), and turnover frequency (TOF) were 0.736 min and 0.02 mmol mg min, respectively. In addition, the fast electron transfer mechanism were investigated and discussed. These results open a new avenue for developing various metal oxide catalysts, which are expected to be very useful catalytic conversions.