Adsorption of Methylene Blue by Halloysite/MnFe2O4 Nanocomposites

Halloysite/MnFe2O4 nanocomposites have been proposed as a novel material which can be used in magnetic and electromagnetic applications. In this study, we fabricated two kinds of halloysite/MnFe2O4 nanocomposites. The XRD and TEM characterizations suggested that ferrite nanoparticles were mainly adhered on the outer surface of HNTs (named as WMH) and in the inner wall (MH), respectively. Both MH and WMH were applied to adsorb methylene blue (MB) from aqueous solutions. The results indicated that both MH and WMH can remove more than 97% MB at a dosage of 2 g L-1 and initial MB concentration of 20 mg L-1. The adsorption processes by both nanocomposites fit pseudo-second-order kinetic model and Langmuir isotherm with correlation coefficient of > 0.99. WMH (19.19 mg g(-1)) shows slightly higher maximum adsorption capacity than MH (18.52 mg g(-1)), contradicts to the fact that the mesopore volume of MH is 30% larger than that of WMH. It can be reconciled by the strong bonding between the outer surface ferrite nanoparticles of WMH and the MB molecules, which greatly enhanced the MB adsorption capacity. In addition, the dimethylamino groups of MB molecules were preferably removed, suggesting the MB degradation by the ferrite nanoparticles during adsorption. Furthermore, both WMH and MH can be easily magnetic separated and recycled. The MB removal efficiency can be maintained at after regenerated for 5 times. Ascribed to the advantages of easily recycling and regeneration, low cost, and MB degradation, the halloysite-MnFe2O4 nanocomposites are potential environmental friendly adsorbents for removing organic pollutants.