Water-soluble Fe3O4 nanoparticles with high solubility for removal of heavy-metal ions from waste water

In this contribution, we synthesized water-soluble Fe3O4 nanoparticles (NPs) with sufficiently high solubility (28 mg mL(-1)) and stability (at least one month) through a hydrothermal approach, and found that they exhibited excellent removal ability for heavy-metal ions from waste water. For the first time, the water-soluble Fe3O4 NPs were used as adsorbents for heavy-metals removal from wastewater. It is noteworthy that the adsorption ability of the water-soluble Fe3O4 NPs for Pb2+ and Cr6+ is stronger than water-insoluble Fe3O4 NPs. Furthermore, the water-soluble Fe3O4 NPs exhibited relatively high saturation magnetization (83.4 emu g(-1)), which allowed their highly-efficient magnetic separation from wastewater. The most important thing is that the water-soluble magnetite as an adsorbent can directly dissolve in water without the help of mechanical stirring or any extraneous forces, which may solve a key problem for the practical application of magnetic powders in the field of sewage purification. Moreover, the water-soluble Fe3O4 NPs show a highly-efficient adsorption capacity for 10 ppm of Pb2+ ions solution which can reach 90% within 2 minutes.