γ-MnOOH nanorods: Efficient adsorbent for removal of methylene blue from aqueous solutions

Nanostructured metal oxides have been of great interest for the removal of hazardous chemicals and dyes from aqueous media. The present work demonstrates efficient and fast removal of dyes from aqueous solutions by using γ-MnOOH nanorods, which are synthesized by the simple hydrothermal method. Uniformly sized γ-MnOOH nanorods are characterized by using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, FT-IR spectroscopy and BET surface area measurements. Adsorption studies of Methylene blue (MB) dye from aqueous solution onto as-prepared γ-MnOOH nanorods are carried out and the effects of contact time, pH and adsorbent dosage on the dye adsorption have been investigated in detail. Desorption as well as regeneration studies are carried out for probing the possibility of reusing the adsorbent. Equilibrium studies showed that the experimental data fits well with Temkin isotherm. Study of the kinetics showed that the adsorption of MB onto γ-MnOOH nanorods follows pseudo-second-order model. This mesoporous material of average pore diameter of 18 nm exhibited excellent sorption properties with a high removal capacity of 89% at 30 °C. The thermodynamic parameters have been evaluated from the adsorption experiments.