Fast Removal of Methylene Blue by Fe₃O₄ Magnetic Nanoparticles and Their Cycling Property.

The fast removal of dyes from aqueous solution and the recycling of adsorbents are currently popular topics in the study of adsorbents. Fe₃O₄ magnetic nanoparticles (MNPs) are usually applied in the preparation of composite adsorbents as magnetic carriers. Therefore, it is significant if single Fe₃O₄ MNPs can quickly remove dyes from aqueous solution with good cycling stability. Here, we report the preparation of Fe₃O₄ MNPs through an improved co-precipitation method, which has the inherent advantage of fast, inexpensive and without requiring the protection of nitrogen or an inert gas. The as-prepared Fe₃O₄ MNPs were used as an adsorbent to remove of methylene blue (MB) under alkaline condition, and then they were characterized by different measurements. The adsorption process was studied by various parameters, such as solution pH, initial MB concentration and contact time. The adsorption of MB over Fe₃O₄ MNPs reached equilibrium in 5 min, and it was observed to obey the pseudo-second-order kinetics model and Langmuir isotherm with a maximum adsorption capacity of 45.43 mg/g at pH = 12 and = 298 K. Furthermore, two simple methods for desorption and chemical oxidation were used to the regenerate Fe₃O₄, and it turned out that Fe₃O₄ magnetic nanoparticles were able to maintain a high adsorption capacity (36 mg/g for desorption and 36.9 mg/g for chemical oxidation, respectively) after 4 circulations.