Adsorption behavior and mechanism of Fe-Mn binary oxide nanoparticles: Adsorption of methylene blue.

Wastewater containing organic dyes has caused worldwide concern. It is thus imperative to develop materials to remove organic dyes from wastewater. In this study, a nano-structured Fe-Mn binary oxide (nFMBO) was synthesized via a facile coprecipitation approach and used for methylene blue (MB) removal from aqueous solution. Characteristic results indicated that the as-prepared nFMBO had a typical wrinkled structure. The adsorption performance of the nFMBO was then investigated by batch experiments. The adsorption kinetics was well fitted to a pseudo-second-order kinetics model, and the adsorption isotherms agreed well with the Langmuir model with a maximum adsorption capacity of 72.32 mg/g at 25 °C. Solution pH was a key factor for adsorption and the absorbent exhibited better removal efficiency for MB in solution with high pH. In addition, it was found that the investigated coexisting anions (CO32-, SO42-, PO33-) did not have a significant influence on MB removal. More importantly, the nFMBO could be easily separated from the water and regenerated by acid elution, and the adsorption efficiency of the nFMBO only decreased to 85.1% of the initial capacity after five adsorption-regeneration cycles. These results indicate that the nFMBO can become an alternative adsorbent for the removal of MB from wastewater.