Ultrasonic synthesis of α-MnO2 nanorods: An efficient catalytic conversion of refractory pollutant, methylene blue

In this work, uniform alpha-MnO2 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 alpha-MnO2 nanorods were confirmed by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The as-synthesized uniform nanorods of alpha-MnO2 exhibit excellent catalytic conversion of toxic organic contaminant (methylene blue (MB)) in the presence of NaBH4 as reductant. The alpha-MnO2 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(-1) and 0.02 mmol mg(-1) min(-1), 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.